Hot water pipes expand when they get hot and contract when they cool off. This movement, the expansion and contraction, causes the pipes to rub against the anchoring straps holding them in place or to rub against the drilled holes in the wood where the pipes rub as they expand and contract. This problem rarely happens with the cold water pipes.
Changing the straps
Improving or changing the strapping on the hot water pipes will often eliminate the problem of squeaking sounds. If the holes in the wood are too tight or too small, then they need to be made larger or try rerouting the pipe.
Who to consult? Plumbers and qualified handymen.
DIY home owners may handle some of the of squeaking type sounds from water pipes themselves. Plumbers are most proficient at handling this type of work, as well as many qualified handymen.