Knocking in wall

[prosc]

I hear a knocking in my bathroom wall when I run water down a drain. It's coming from the drain side and not supply. If I run the water into the sink with the drain capped I hear nothing but when I open the drain, a few seconds later the knocking begins. It's been doing this for a very long time (years). The bathroom is 5 years old and on the second floor of my house. The supply lines are plastic and up to code. The drains are PVC.

 

[Mr_David]

The drain pipe is tight against the wood, usually where it passes through the floor.
As the pipe expands and contracts it rubs on the wood and pops.

When they are really loud and annoying the only way to fix it is to open the wall and drill/chisel/cut the wood away from the pipe.

We use ABS pipe here for drains and that is what we commonly call an ABS TICK