How can I stop a bathroom waste pipe making a clicking noise?

Interesting one... We had a similar problem and found that lagging the pipes significantly reduced this. We guessed that the clicking noise was caused by changes in rpessure and temperature moving pipes against each other and against floor boards / joists. Problem is that this does mean you will have to lift floorboards.

Ian
May 2008

This noise is the pipe expanding due to a temperature rise when water is flowing down it. If the noise is from under the floor, I would say the pipe has been fitted very tight to the joists, and the noise you are hearing is the pipe moving against the joists
Only way to be sure is to lift the boards and have a look. Putting and insulating material between the pipe and any joists it touches should help. DO NOT cut too much of the joist away to create space!

John
May 2008