It's probably just the water pipes rattling around in the wall. I know that my water pipes rattle around because I can see them on the floor joists in my basement.

Could it be some odd “water hammer” situation? If anything might need bleeding, doing that might improve matters.

It could be pipes rattling from poor pressure as it tries to pump water into the toilet tank. Could be that someone closed the valve at the wall so water is struggling to get through. Have you tries opening the valve under the toilet a little?

Could be a vibrating pipe or a in wall air valve.

1. When pipes run hot water they sometimes make clicking or knocking noise as they expand.

2. It’s possible you have flexible pvc pipes that can move a little when the water pressure increases or decreases.

3. Any of the things already listed.

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Sounds like expansion and contraction due to temp differential.

I am imagining a poor copper pipe, alone in the wall, trembling and sweating from the massive effort of filling a giant toilet tank all by themselves.

In reality, though, pipes don't "vibrate from the struggle." Indeed, pipes don't "struggle" at all. In this case, I'd put a few bucks down on the "thermal expansion" theory.

This is your answer.

Yep, ours have been doing the same thing for over a decade. It's like whale and ocean sounds to me now. I'd be worried if it stopped at this point lol

When the lines were ran during construction the holes that were drilled through the wood were too tight. As the pipe expands and contracts you will get a ticking noise that sounds exactly like a drip. As the seasons change and the humidity of the house changes the sound can come and go.

I have that when I run the sink taps in the 2 piece bathroom off the master bedroom. It is the pipes contracting and rubbing on a 2x4 in the wall. When I push on the wall it stops for a short time and starts up again until the pipe warms up.

Thanks for all the input, I'm relieved nobody said "oh yeah, that's a leak." This is our first winter in the house so I'll be interested to see how the temp and humidity changes affect the sound. I don't recall hearing anything last summer but can't really say I was listening either.

It's grandma living in the walls.

If it was a leak it wouldn't only be heard when the water is moving truth the pipes. It would be constant. Most leaks aren't audible either, that's why they can be so destructive.

Thermal expansion/ contraction. Same thing in my house. Hard to fix without opening walls as a rule. Not uncommon in production builds. Nothing to worry about.

If your house was built in 2001, I suspect it has PEX pipes, not copper as others speculated. In the end it’s the same issue, thermal expansion or vibration from pressure changes.

Check out this video: https://youtu.be/Xy9aJdX5xF0

I too am relieved nobody said it's a leak because our house that we moved into like 3 years ago has a very similar tapping noise, happens when we shower and sometimes with our sinks. I haven't seen any water damage in all this time, so was hoping it was just thermal expansion. Definitely not water hammer, that's pretty distinctive sounding and really only happens right when the water is turned on.

We had the same problem, water pressure too low and replaced our pressure tank and all is good