Foghorn noise when turning on the shower.

MrsEMG

I have a foghorn type noise whenever I turn my shower on. It sometimes lasts for a few seconds, sometimes a few minutes and then it stops. It goes away if I run a tap or flush the toilet. It doesn’t happen when any other hot tap it ran, just the shower. The shower has two heads and started after I used the smaller head for the first time so thought initially that it was air in the pipes. I get more of a squeak when I use the smaller head than a foghorn. Any idea what it could be and how to fix it? Thanks in advance

Chanes

Water hammering? We had a toilet that sounded like it was going going to shake pipes out of the wall but it was a dodgy washer on the inlet. That would be my untrained guess...someone will know better!

[Deleted User]

Have you got an unvented system? Sounds like an incorrectly inflated expansion vessel to me. Not sure why that would happen only on one outlet though.