Every time I flush one of my toilets, a loud knocking sound comes from inside the tank. You can hear it all over the house. It is particularly bad when there is water running in another part of the house. Before it would just happen when there was water running somewhere else, but now it happens as soon as the toilet is flushed. Any ideas?

Which ballcock is yours? (see images) Let me know\, Tom

The image on the right...

Shut the water off to the tank, remove the three screws fro the top of the ballcock and pull the stem and float ball assembly up and out. Try the washer out and turn it over, being sure to seat it in firmly. Now place a pan over the ballcock and turn the water back on for a few seconds to flush everything out. Reassemble and give it a flush. Noise all gone? Good luck, Tom

Worked great! Thanks for the help!