Sounds like pipes moving from thermal expansion.

There is not a lot you can do without opening walls to locate the place the pipe is rubbing (usually a bored hole in framing the pipe passes through) and then slip something in the hole to allow smoother movement.

The fix is often as simple as a few layers of wax paper wrapped around the pipe and slid into the hole in the wood.

The you get to patch the wall.

the neighbor was suggesting something that fixes old fashioned hammer arrestors, if you really really empty the pipes for a long time. Do you know what hammer arrestors are? web search this and post if it sounds like it may be relevant.

Did anything else change recently in the pipes, fixtures, plumbing, or studs? How old is the house?

"Moaning" is not water hammer.

Water hammer arrestors are gas filled devices that help absorb the momentum of moving water when a valve is quickly closed.

The gas is compressible enough to absorb the energy of the moving water.

Agree with brickeyee that this is not water hammer. I would be surprised if arrestors had any effect.

If the sound is what I think it is, it is likely confined to a specific location -- probably a valve.

For example, when a toilet flush-valve gets calcified "just so", and the water volume and velocity through it is "just so" it can "moan" or even scream. It's a resonance frequency thing. Cleaning or replacing the valve solves the problem.

Can you say if your symptom is actually from "the pipes" generally or is it coming from a particular valve or location?