A number of years ago I remodeled a mother-in-law apartment in my basement. The cold and hot lines were replaced with pex tubing. Recently the tenant told me there was a lot of intermittent 'groaning' from the pipes in the bathroom when he turns on a valve (hot or cold) or flushes the toilet. It also occurred when the washing machine was running. I assume that this is due to air in the line. The upstairs living area is served from the same lines and we are not experiencing the problem. While the tenant was out I opened all of the valves in the unit and let them run but did not hear any noises or get air coming out.

Any suggestions on how to trouble shoot and correct this?

 

Cavitation can cause pipes to shake, which is why they are usually restrained by a clamp. You would have to narrow down where the pipe is. Can't really suggest much if it's innaccessible or inside a wall.

 

Water hammer? I imagine a PEX pipe "groaning" could describe a buzzing sound. I get that in copper pipes feeding a bathroom from time-to-time on the same branch as a washing machine. Most times it is caused by the toilet fill valve that has a worn gasket. It stops when I open another faucet on the same line.

Maybe you need water hammer arrestors.

 

It is my understanding that water hammer is noticeable when a valve is shut and the sudden increase to static pressure causes the 'hammer.' Cavitation is possible but all of the pex is attached to the studs. Also, pex should be move forgiving than copper since it is flexible.

My tenant just told me that flow is reduced when he turns on the valve and the noise is present. I am starting to think it may be an obstruction caught in a valve.

 

Turn the shutoffs off, take the supply pipes off the fixtures and then grab a bucket and turn them on full blast and see if you can recreate the noise manually. We can't narrow it down for you, you've mentioned every fixture... so start narrowing it down. Check them one at a time.

If you've been there and can't recreate it, it's not very likely we are going to be able to figure it out either.

 

That type of groaning is often caused by a worn washer in a valve somewhere. The water running over it causes the vibration and often incredibly loud noises.

It could be any valve with a washer in it (shutoff valve, washer valve, toilet fill, sink faucet, PRV). Since it seems to happen with any bathroom fixture, I'd go upstream a bit. Is there a valve that shuts off the whole bathroom? And for what it's worth. ball valves shouldn't have the issue.