On Thu, 27 Dec 2018 18:32:38 +0000, Jeff Layman wrote:

If the noise returns, I'll try partially closing the tank isolator valve
first to see if that helps, as that's the easiest thing to do. If it
doesn't, I'll try the "yoghurt pot" dampener on the float arm.

Had this as well right PITA to cure. I think I ended up bracing the
incoming, plastic and very poorly fixed, pipe into a position where
it didn't resonate. Turning the isolator down really on affected when
in the filling cycle the noise appeared and its frequency.

But if all those fail, I think the easiest thing is to fit a Torbeck
valve instead of the standard float valve.

If you do make sure the over flow can cope with the much higher flow
rate of a stuck open torbeck...

--
Cheers
Dave.