Leaky Drain Pipe in Wall

When I use the 2nd floor drains in the bath or sink, I can hear a drip in the wall. It starts out relatively fast; one drop every second or so, then slows to a drop every 3-5 seconds. I think all the drain pipes are PVC. There is no visible water damage on the wall where the main waste comes from the second floor, then flows out to the septic tank. Any advice on how to locate (and fix) the drip without tearing open the wall would be greatly appreciated. Thanks!

Since you haven't found any water damage, I suspect you may be hearing water inside the pipes. PVC/ABS do not absorb sound well. If you do have a leak, it's impossible to tell you how specifically how to find it because every situtation is different. You will just have to look everywhere the drain can be seen, punch small holes to peek inside, and listen carefully to pinpoint the leak. As far a some magical method of working inside a wall without opening, sorry, there is nothing. In the first place, if there is a leak, the water has damaged the drywall and that will have to be replaced. Secondly, the only way to repair PVC/ABS is to cut and install new fittings. You can't trust the quick-fixes sold in the box stores, but even to use them you would have to open the wall.

Is it a leak/drip sound or a tick ? If it's a tick it is most likely that the pvc is tight against some wood or duct etc. Hot/warm water will make the plastic expand ,,if it has nowhere to move you hear the ticking as it expands against whatever holds it. Soon as the pipe cools back down and contracts to normal size ,,,it stops. No worries,,,just an annoyance.

tick

If you were to listen very carefully, you would probably also hear the ticks later. They would be fainter and further apart since the pipe cools down slower than it heats up.