Unusual Plumbing (Toilet) Question

[FLHTPI]

This is a strange problem:

I recently noticed that when I turn off the water in my bathroom sink, the "pipes" start banging. I can get the banging to stop by opening the same bathroom faucet for a few seconds. When I do, the water comes out in spurts, then evens out and the banging stops.

I've actually isolated it to this: When I turn off the water, there's something that gives my toilet tank a little "jolt", (maybe a vibrating pipe?), and the float arm starting vibrating, which is what causes the banging.

I couldn't possibly be making this up.

This has not been easy to describe, and I'd be very grateful if anyone has any thoughts on what I can do.

Thanks!

[Speedy Jim]

No, you're not making it up.

Some brands of toilet ballcock exhibit this when they are worn out. Either replace the ballcock or, if you can find repair kit, repbuild it. The one I've run into most is made of white plastic with the brand "Coast Foundry".

Jim