I have a partially finished basement in a 15 year old house. From the
unfinished utility room I can see between the basement ceiling and the
ground floor floor. I have the AC pipes and new copper water pipes in this
space running the length of the basement. It is slighly less than a foot in
height.

In the basement I hear a dripping sound or a clicking sound on a fairly
constant basis. Every 30 seconds or so. This has been going on for as far
as I can recall; several months. There is absolutely NO sign of water or
other codensation. I figure after several months if it was a leak I would
have seen something by now. The floor above is carpet on top of plywood.
Could I have gremlins running around in the AC pipes? Water condensing in
the AC pipes? Or is it just the floor settling?

Anything I should be concerned about?

Thanks