When the shower runs upstairs in our home we hear what sounds like a leak or a tapping sound downstairs. We have no signs yet of water damage, but want to know if it's a leak or just the pipes contracting or expanding? Not really sure what it is as we have left the shower on and the noise tapping/dripping sound is very inconsistent.

Drip and Tapping are two different things: Drip means you have a leak somewhere in the wall or ceiling while Tapping means you may have water hammer. Investigate some more. See if you can find out if it is water leak. Question: any sign of wetness on the ceiling ? Back to you. Milo

Stop by your local home fixer upper store and pick up a 1/2" PVC threaded pipe cap. Remove shower head and screw on pipe cap. Screw on hand tight, doesn't matter if it leaks a little bit. Turn on show valve. If you hear dripping sound, you have a leak in supply piping some where.

To check drain piping, plug shower drain and fill shower pan with water. Use a bucket and get water from another source. Wait. If you hear dripping you have a problem with shower pan. Remove drain plug. If you hear dripping during and after draining, you have leaking drain pipe.

After that you will have to look for leaks through tiles and around shower pan.

You can also get a popping sound if you have a hot water supply pipe that is rubbing against a joist or other structural member as it heats up and expands or cools down and contracts. You should get that sound only when the hot water is running and only when it first starts and after it stops. You would probably get that sound when hot water is used at the sink but not necessarily.

Outstanding checks and solutions by Harold. I would click the "helpful" button but I'm afraid to touch them. Great answer Harold, covering all basis, Tom