One issue we run into a lot is the mysterious tapping sound whenever a fixture is running water. This sound usually indicates that there is a water leak either in the ceiling or in the wall. Typically this will show up as a water stain near the source of the leak. Sometimes this sound is related to the thermal expansion of drain lines from cold or hot water running through it. When unsure if this sound is leak related or thermal expansion related, then a simple DIY test can be done. Run hot water from the faucet that is creating the tapping sound. If the problem is thermal expansion related then you will eventually hear the tapping sound stop. Once the drain line reaches the full expanded position, then it will no longer make noise. This sound occurs when the drain line is touching a wood member of the house. During the pipe expansion/contraction, at each shift moment, a sound is made from the pipe rubbing against the wood. The only solution to this is to open up drywall and insulate all points of contact.