Tapping sound in Shower Wall

[armenhamer]

This morning when the water finished filling up in the toilet (main floor) after flushing I heard a few tapping or scratching sounds coming from the shower wall. I flushed the toilet in our basement and stood under the main floor bathtub and heard it again. It seemed to happen when shutting off the bathtub faucet, sink faucets and after a toilet flush. So far I've shut off the main and allowed the faucets and toilets to drain twice. Still the faint tapping sound continues. The bathroom with the issue was remodeled a little over two years ago. The house also as of last november has new copper plumbing. For further info, from time to time I've notice some water coming out of the offending showers faucet. It will just randomly drop a little bit of water out. Any thoughts or ideas on what could be going on here?

Thanks!