Loud noise and knocking when I flush toilet!!!

[janbou]

Recently in my upstairs toilet, every time we flush the loo it makes a groaning noise, the pipes sometimes knock as well. Have tried adjusting water pressure, but this only short fix....any ideas???

[parkesquay]

I had the same problem and it it was only because I recently refitted the bathroom that I came across a solution to the problem. The vent that is attached to the soil pipe system had tended to go into vacuum mode and thus there wasn't sufficient air pressure to operate properly(this is a tube similar size to the soil pipe that quite often goes vertically into the loft and at the top of it is a vent attachment). Now as it so happens mine ended behind a false wall in the bathroom and during a recent the refurbishment I needed to get to the shower pipes behind the false wall. Quite by chance I observed that the groaning noise from the toilet no longer happened. So I came to the conclusion that because this vent was effectively sealed(behind the false wall) from an air flow that the vent was effectively in(or tending to be in)a vacuum. After I put things back together I put a piece of small overflow pipe at the top and bottom of the redone false wall and the problem no longer exists..so far.
I am not a plumber so please excuse the lack of correct terminology.

[parkesquay]

I should have added ,if it is not too obvious ,that the piping I fitted top and bottom extends out of the flase wall into the normal air flow.