nicktheplumber
jenga,
I read and reread your post with great interest, and I can’t make sense out of your problem. How do you know the sound is coming from your drainpipes? The only way water can enter the DWV system is by going into a fixture drain… Do you have leaking faucets or a leaking water closet tank? Sputterring faucets indicate air in your water supply pipes.
NtP
