PVC slow drip

I currently have a PVC pipe (drain) that extends from my laundry room that has started to leak (slow drip) -- its obvious the water is coming from above (I can see it on the wood where the PVC meets the floor in the basement). Just looking for some suggestions prior to the cutting of the drywall upstairs (I assume the leak is from either the utility sink or the washer as they appear to connect to this main PVC behind the wall).

The part that concerns me about this is the leak leaks even if the washer / utility sink are not on -- its just a constant slow drop -- none of the copper pipe is leaking/etc -- any help is highly appreciated!.

Paul

B4 you cut wall:

I don't think it's the fixtures bkz they wouldn't leak when off. To be abs certain, you cld disconnect their traps from the wall and wait to see if the prob clears up.

Does the dripping happen during colder weather? That drain is likely vented, which means it up past where the junctions are for your fixtures and out the roof. Cold air can condense in the top of the pipe and drip down. If the flashing around the pipe isn't proper, water could drip down the outside of the pipe. Unlikely, but a poss.

Anyway, I'd do some more investigating and eliminate individual fixtures b4 you cut.