Bath room single handle mowien faucet . When I turn on the hot water I can hear Water drops in the wall. it stops immediately when I turn off the hot water. It does not do it when I turn on the cold water. there is no water drop sound when the faucet is turned off. Only when I turn on the hot water side. Cannot figure out with water pressure constant why it only leaks when the faucet is turned on to the hot side?

im no plumber but sounds like you may have to open wall up if your getting water in wall dripping .Can you see any water stains in ceiling in basement if there is a basement

It could be as simple as thermal expansion of the hot water supply piping. When hot water is running, the pipe expands and could be rubbing up against a joist or timber. If you have access to the piping from below, you might be able to move or add a pipe clamp to fix it. Otherwise, I wouldn't worry about it, especially if there's no visible signs of leakage and it stops when the hot water valve is off.

It's more than likely not a leak, but expansion of the hot water piping or drain piping, rubbing against the framing.

ditto

ditto

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"Measure Twice & Cut Once" - Retired U.A. Local 1 & 638

Expansion it is.