I am hearing a rather loud "tap" sound when I run the top level fixtures. It sounds like it might be coming from a wall. From where I can hear it, the drain runs straight down into an expansion joint, where several other drains tie in, and then down into the sewer.
I have looked for signs of water in the basement but haven't seen or been able to feel any, from where I can reach my fingers up into the hole that the 3" drain comes through. Is it possible that the pipe is tight against the wood framing in the wall and the sounds I hear are the groans of thermal expansion/contraction?
The sounds stop when I stop using the drain, but I've noticed they seem to give one last "tap" when I step on the floor near the wall in question.
In my house in a COLD climate the vent pipe/stack from the sink/tub goes into the attic and when I run hot water heat rises up it and it expands/contracts it and makes noise. Sounds like an expanding/contracting noise to me. Houses/wood expands/contracts with the seasons/changes in moisture so it may come and go.
"Cut it twice and it is still too short".