We get a rumbling in our pipes whenever we turn water on, especially when the washer is doing its rinse cycle, and later in the evening when we turn on the kitchen sink.

I recently fixed the pressure reducer valve, which dropped the incoming pressure from 80 psi to my set value of 60 psi. No help. Then I installed "mini water hammer arresters" at the washing machine hot and cold. Marginal improvement.

Does not seem to matter hot or cold water. The rumbling lasts about 3-4 seconds, then quickly tapers off.

If it is just normal rumbling that will not hurt the plumbing, I don't really care. It is an old (20's) house, so I am trying to baby it to keep the plumbing sound.

Thanks!

Have someone create the rumbling sound while you keep your hand on the reducer and the incoming main valve, I think one of them is vibrating. BTW 60 is still a bit high, I shoot for 45 psi

So, nothing to worry about?

If a washer or diaphram is vibrating it is failing and needs repair so I would worry.

Old post, new insight
Had a new water heater installed, and they put in a hot-water expansion tank at the same time.
Voilà, the problem is gone.

Old post, new insight
Had a new water heater installed, and they put in a hot-water expansion tank at the same time.
Voilà, the problem is gone.

Perhaps the expansion tank acts to prevent water hammer, at least on the hot side.