On Fri, 15 Jan 2021 08:25:56 -0000, "Brian Gaff \(Sofa\)"
wrote:

It very much depends on where its actually coming from, both ideas here
could be the case, and my neighbour had a pump that occasionally shifted and
made contact with a wall, transmitting the motor buzz all around the house
and also here next door.
Brian
I had similar symptoms with the pump, got annoyingly loud after a few
years. Had a new pump fitted, totally quiet again, and rads getting
warmer, faster. Dismantled the old (10 year old Grunfos) pump, just
separated the motor from the cast body, and found that the impeller
was almost totally clogged up with hardened "sludge". The design of
the impeller has narrow passages between its input and output edges,
which can get easily clogged. I could have got away with just cleaning
it if I'd known about this.
Have now had the system power flushed and a Magnaclean filter fitted.