Our pipes make a loud roaring noise when the toilet tank is flushing
and re-filling. Our apartment had been empty for a few months when we
moved in and initially the noise happened when running the hot tap.
After a while this cleared up but then some people moved in upstairs
after that apartment had also been empty for a few months. It started
again but this time whilst flushing and re-filling.

It is the same noise (sounds a bit like a go-kart engine) so I can't
see how it could be un-related but cistern noise solutions don't sound
like they would work for this since it was originally related to the
boiler.

It seems to be getting worse the more we use the toilet - if anyone
has any ideas it would be much appreciated.

Thanks.