I think I know what you're describing. Be certain you've identified where it's coming from. Could be supply valve in the wall but I doubt it. I'm suspecting it's coming from toilet valve innards. Changes pitch as the tank fills, doesn't it? Please advise.

Yes Aslo, its coming from toilet/bathroom area; does not appear to be int ehwalls and down below where the piping is. As to the change of pitch, well, not really, and also, it seems to come and go. I recall, it was happening about 4 months ago or so, and what I did was empty the tank, and cleaned out the thing with rags etc. I t seemed to work; until now again.

Also, you may find interesting, I have the ame toilet in another bathroom, and this started to do the same thing,, so I cleaned that one ot and it has stopped, and has not picked up again, at least for now..

Thanbk you

Jim

Bingo. Calcification-induced resonance frequency amplification. (Don't get excited. Just made that up.)

Basically, crap in the water adhering to internal components reaches an obstruction level where the water-flow itself induces a vibration which becomes audible. Generally increases over time.

Not familiar with your toilet's guts. Can you pop the top and clean it out? (Not to get excited. It WILL return after a while.)

Do you know water hardness? Soft water can delay the onset....sometimes indefinitely.

Sure, thank you very much. We will get to work.

I would replace the valvecap on the fill valve. Order a backup to have onhand. Search "Lavelle #R528 Korky ValveCap Assembly", $2 + s/h. It's also easy to replace.