For a while there has been a persistent knocking in the drain lines of the plumbing system in my townhouse. From the moment I turn on the faucet to well after the water has stopped running there is a "knock" within the walls.

I've recently remodled the bathroom but made no changes to the drain lines except to relocate the shower drain.

Even after 30 minutes or more there is a knocking at about 30 to 45 second intervals which makes falling asleep difficult.

This is VERY annoying! Please help.

Does this happen if you just open a cold only valve? Most bathroom faucets use a mixing cartridge valve so you are using some hot and some cold if you just pull the knob open in the central position. Hot pipes expand and can cause a bumping or knocking sound. Rotte your knob to cold only then open , no nise I'mguessing, back to you.