I've got a primary and backup sump in my sump pit - both have check valves below the point where they connect to the single discharge line that pulls the water out of the house. In the past week, I've started to hear a very slow dripping sound in the sump pit - it sounds somewhat like a leaky faucet. The water level rises, but (a) I don't see any water coming from the internal perimeter drain and (b) I don't see any water dripping anywhere in the pit.

What might be causing this dripping sound? Is it possible one of my check valves is bad and the water is leaking down the pipe and into the pit? Other ideas?

Thanks!

Water dripping into a floor drain from an a/c condensate drain? A faucet dripping upstairs into a drain made of plastic? Pvc transfers sound a little too well for my taste. I don't like sitting under my upstairs bathroom for that reason alone. Makes me jump when the toilet flushes. Reminds me of trying to work on a commercial sanitary stack in a nursing home. You don't know when it is about to be flushed, but it happens more often than you want it to.