Noisy Drain Line

[darb]

I have an Aqueon RR with the Aqueon overflow kit that is making a lot of noise which seems to be as a result of air and water mixing.

It is running a Mag 7, so pumping about 400 gph and the noise seems to be as a result of the air and water entering the drain line below the bottom of the standpipe in the cabinet.

The setup was previously plumbed with flex PVC in the same manner and going from memory, it seemed to be less noisy; although it is in a room with hard floors and no carpeting now.

Any suggestions for noise reduction?

My only though it to use pipe insulation which is treating the symptom and not the cause.