I'll try to get everything in here, yet be concise.
This is a 3-story building, plus basement/underground parking. I'm on the 2nd floor, studio. Same layout above and below. Exterior wall to balcony; all others interior. Kitchen and bath share a wall (and also run along interior wall for hallway). The drip sound is from the wall between the kitchen and bathroom.
Kitchen sink is on an island "wall" not attached to the "problem" wall. Bathroom sink and toilet are on the wall opposite the "problem" wall. I was thinking there wasn't any plumbing in the "problem" wall, but my mom pointed out the sprinkler system. And, duh, the shower faucet is on that wall (drain is in middle of tub, though).
The drip is extremely intermittent. It seems to occur at any time of the day (or night), and does not appear to be related to water running or having been run recently. It SEEMS to be coming from/hitting somewhere near the ceiling. Also, several feet to the side of the shower faucet. When I hear it start, I've listened to see if anyone is running water (even going upstairs to listen) and there is never water running.
I've talked to the guy upstairs and he also hears it. I haven't yet asked him if he can pinpoint "where"--as in, does he hear it towards his floor or not? (to 'correspond' with my sense that it is near my ceiling) I haven't talked to the guy on the first floor. If he doesn't hear it, then....well, it helps isolate the problem, I guess. Oh--I've listened in the hallway downstairs and not heard it. But I also listened in the hallway on the 3rd floor and did NOT hear it; but when I asked the guy, he did hear it inside his apartment.
The building is about a year old. The drip/sound occurs during the summer and now (so, when hot or cold outside). I've seen no evidence of water damage on either side of the wall. I first heard it....about 5 months ago. I wasn't here before that (I am first tenant in this unit). If it's been doing it since construction, I'm not sure if that would be enough time for damage to show on the "living" sides of the walls? I would think so, but....
Obviously, with sprinklers in the wall, there are pipes. But I can't think why those pipes would have water moving through them 2 or more times a day. Wouldn't water just sit in those pipes until needed, if ever needed?
The sound -- like big drops. Nearly always the exact same speed, although I think a couple times it was quicker. It lasts anywhere from a minute or two, to 15 minutes or more. I'm up all night--it often happens in the middle of the night. No one else is up and running water, and I would not have run the shower for...hours.
I'd like to figure out WHAT this is, because I really do not want them coming in here to tear out the wall to try to diagnose it. There is no maintenance person on-site, so I can't just get him/her when it decides to drip.