What could be causing the mysterious banging every forty minutes in our house from the area under the AC, even though the AC isn’t always on and the disconnected swamp unit has no power?
Asked by Matthias Leclercq 
6 months ago
Last Updated: May 27, 2024
So, we’ve got this weird banging noise that happens in our house every night around every forty minutes. It starts at 1:45 AM and goes until about 3 AM. The sound seems to be coming from below the AC unit, but here’s the thing – the AC isn’t always running when we hear it. We also have a swamp unit right next to the AC on the roof, but we never use it. So, after we heard the banging, we completely disconnected the swamp unit from the power source. Still, the noise persists. Any thoughts on what this might be? We just moved in here a week ago and this mystery is driving us crazy!
Could it be an animal? Try setting up a camera.
Wow, that’s scary!
Could it be from the previous owner? :O
Do you think it’s coming from a dryer or a washer?
Looks like your house is haunted, buddy. We’re not sure how to help.
I made that comment before I listened and it’s so much scarier with the sound OMG your house is definitely haunted
Totally agreed!
Is the sound always consistent? Does it happen at the same time every night? My guess is that it might be related to a water softener or heater schedule. Loose water pipes can create interesting sounds.
That’s exactly what I was thinking because it all lines up with the same timeframe…
Have you gotten the AC checked out? It seems like this might be happening more frequently, but you only notice it at night when it’s quiet. It sounds like something might be loose to me. You know how a washer will make a banging noise if it’s out of balance until it starts spinning faster and stops banging? I suggest starting by having the AC professionals check it out. Show them the video.
Our neighbor’s AC was making terrible noises, turns out, several bolts had become loose 🤷
Oh my gosh we couldn’t ignore this even if there was an earthquake, it’s ridiculously loud. I mean downright scary loud
Hmm… it might be related to the water lines (similar to the softener mentioned by someone) OR…..if it only happens at that specific time, go up to the attic to try and pinpoint it more (?) Personally, I would call an AC company to come out, explain the issue, and show them the video
My initial thought was the same, but the timing seems off. I observed our RO lines banging last night, so it’s definitely a water piping or water hammer problem. I’m just unsure why our RO system would trigger this.
It’s strange how consistent it is. Happening at the same time every night at regular intervals. You’d expect it to be more random if it was the AC or water heater. Those units operate based on need, not a fixed schedule. It seems like something might be off balance causing metal to hit against a cabinet. Do you have a water softener that cycles every night? It shouldn’t unless your water is very hard. It could be the softener running through its cycle and causing water hammer. Do you have pipes in that area? Maybe an air exchange unit set to cycle. Can’t think of anything else that operates on a timer. Check the pipes, have someone rattle them near the softener while someone else listens for the noise. Or manually cycle the softener to see if the noise happens. It could also be something environmental like heavy truck traffic or passing trains shaking your house. Start with the water softener to see if it’s the source. If it is, consider getting a new one or servicing the current one with water hammer arresters. Good luck!
I appreciate your help. There’s a softener that we’re not using! We’ll deactivate it. This only started happening after we installed our RO system, it wasn’t an issue before.
I also wanted to mention that our water is incredibly hard since we’re in Arizona. It’s really tough water. I’m just confused why it’s acting this way with our RO system now, when it wasn’t before.
Hey Chris! Oh man, Arizona water, am I right? Once you have everything sorted out, definitely consider using a water softener. Otherwise, you’ll start noticing hard water buildup on everything – and I mean everything. I speak from experience! Get ready to have CLR as a frequent visitor. 😉
Oh, we’re aware of that. The system is pretty old and not a top priority for repairs at the moment (it’s also turned off). We don’t use the tap water anyway, so it’s been put on hold.
Is happy to assist. Yeah, I don’t understand why the cycle would make a difference either. Based on what you’ve described, it sounds like your drinking water is almost as thick as wet cement. 😮 While I’m no expert, I have a feeling that your resin tank is on its last legs. It might be time to reach out to the water softener professionals and see if it’s worth repairing or if it’s time for a replacement. Another possibility could be that your water main is so clogged with minerals that it’s causing a restriction, which could be affecting the water softener’s performance. It’s just a hunch, but it might be worth looking into or discussing with your plumbing experts. Best of luck, happy to lend a hand.
Just wanted to add that it’s not because of the softener. It’s completely bypassed and turned off. We’re really stumped, it must be something else
So I looked up water softener hammering on Google. There are a few possibilities for causing water hammering, like high water pressure (which I don’t think is the issue here. Is your water pressure low?), a resin tank that needs replacing, a calcified power head, blocked Venturi valves, or inlet valve, a stuck float, clogged or restricted water lines, drive motor failure or damage – all of these can cause water hammering. So when you bypass the water softener, the noise stops, right? The hammering only happens when you try to use the softener, correct? And you’re not getting soft water when you use the softener, right? If that’s the case, based on what you’ve told me and what I’ve read, it might be time for a new water softener.
Hey, just to clarify, the softener has been bypassed this whole time. It’s definitely not because of the softener. And this is all on a schedule
Is nuts, but ok, just trying to get up to speed. It seems like the softener bypassed is not making soft water. Have you checked if the power is turned off to the softener, so there’s no way for it to run? I’m just trying to remove noise sources. If you power down the softener, does the noise stop or continue? Also, does your HVAC have an air circulation setting? I was thinking about mine, it cycles the blower fan every 2 hours for about 10 minutes to freshen up the house. Maybe your blower motor or fan is out of balance. And don’t forget about other noise makers like freezers, refrigerators, and hot water heaters, they can make all kinds of noises too. Good luck finding the source of the noise!
It sounds like there’s some serious water hammering going on in the pipes. The softener isn’t getting any power, and it seems like the water company might be involved. The noise is really loud, especially around the master bath sinks and kitchen. It’s even worse with the RO system connected. The noise has toned down a bit now, but it lasts longer. It’s hard to describe how loud and extreme it is. And just to clarify, our fridge isn’t even here yet, but it doesn’t seem to have any issues. This definitely seems like a plumbing problem.
I’m curious, Chris, about what might be causing your pipes to make noise in the early morning hours. Have you checked the water pressure in your house? It might be worth looking into getting a pressure reducer valve or water hammer arresters. Good luck figuring this out, at least now you know what’s causing the issue.
Sounds like a demon is trying to break free
Man, this noise is really getting to me
Likely some kind of creature
I initially thought it might be the water softener.
Can you believe we’re experiencing a water hammer under the kitchen sink from our trusty RO system that we’ve had for years? What could possibly be causing this strange schedule of 1:45 am, 2:24, and then 3 am? And nothing during the day!
Sounds like there might be a poltergeist around.
I just found out that newer pumps in certain systems can actually learn about the times they are used the most or least during the day and adjust their activation accordingly. For example, the hot water recirculating pump in a property I oversee learns about the typical shower or laundry times of the homeowners through temperature and pressure sensors. There might be a component in one of your systems that is acting autonomously in the middle of the night. The new RO filter you installed might have a flush mode that kicks in at those odd hours. It’s similar to how your cable box decides to do updates and resets when you’re not likely to be watching TV. If you’re up for it, you could try turning off and unplugging each system in your home to figure out which one is causing the noise through a process of elimination.
Well, the RO system isn’t exactly new; we’ve had it for quite a few years, just not in this house. The softener doesn’t seem to be running, but it’s also not bypassed, so that’s our best guess. We’re just not sure why it’s causing the hammering noise when the RO system is connected.
Hey, the kitchen faucet at my place is starting to show some wear and tear. Every now and then, it doesn’t shut off completely, so a little water drips out along with some air getting into the pipes. This results in some banging sounds in the pipes, though it’s not constant.
You could try leaving a faucet slightly open, it could be due to pressure building up.
Oh my goodness! Maybe consider putting a for sale sign outside and making a quick exit 🏃♀️
Recently purchased it like a week ago lol
Edit to include that it’s NOT the water softener since it’s completely bypassed. I have no clue what’s happening
Burn some sage.
Oh, just those time frames? What’s even in that area?
Yes, ! And this photo shows the kitchen sink. Our reverse osmosis system was causing a major issue under that sink. We fixed it, but now the bathrooms are experiencing the same problem.
Alright, let’s try to narrow it down. If the noise is consistent every time, it might be a motor like a fan or pump. I recommend turning off most of the circuits in your breaker box, leaving only a few lights on right before the noise is expected. Did it stop? If yes, then it’s likely electrical/mechanical. If not, then it could be something else. Give this a shot first. It’ll guide you on what to do next. Slowly turn on the breakers until you identify the source. If it’s not something you can turn off, the next possibility is that it’s an animal. Many nocturnal creatures like to nest under houses and follow a routine. I have a feeling it might be a blocked pump or fan trying to operate.
Hey , it’s definitely a water hammer issue. It seems like something the water company is causing. We disconnected everything last night and only heard a slight pounding in one specific area, not too loud.
Hey , if you have a water hammer making that much noise, you might want to check or install water hammer arrestors in your plumbing. They are mandatory by code now and can really help, especially with copper pipes.
Hey , it only gets noisy when things are connected, and it happens three times a night. Any thoughts?
If we’re talking about your water supply, there could be a few reasons for that noise you’re hearing. The first step is to head out to the street and turn off the water at the meter for a couple of hours when you’re expecting the noise. If it stops, then it’s likely an issue with the city supply. If not, try closing the valve on your water heater and disabling the power or gas to it for a bit. No timers or recirculation system, right? Grab some pliers and shut off the water overnight. That should help determine if the problem is internal or not.
Clarified that the water supply is private and gravity-fed, meaning there are no pumps, timers, or maintenance required. Additionally, no commercial accounts are allowed.
Sure thing, Chris. Sounds good to wrap it up early one night.
So, we contacted the water company and it turns out we are actually using a gravity-fed system! They’re just as puzzled as we are and we can’t find any timers that would make sense in this situation.
This really scared me, I hope you can figure it out soon because that noise would drive me crazy
Quick update, it turns out it’s the irrigation system! The timer appears to be malfunctioning, turning on at random times. This explains why we experience low water pressure in the house when it’s running, and why there’s a hammering sound under the kitchen sink when it shuts off.