We have a 3" PVC pipe in our bathroom that runs up to the attic. The water heater, AC unit and other items are all attached to this vent pipe "system".

It runs about 10' straight down a wall and then has a 45 degree angle. This is where the "drip" sound occurs.

How do I insulate it so that it isn't so loud? It is heard from both sides of the wall (bathroom and a bedroom) and is driving me crazy.