When I flush, the toilet tank overfills above the siphon mechanism, which makes a pulsing swishing sound. I turned the water off at the wall, but when I turn it back on, the siphon mechanism makes loud pulsing noises again and the water heater in the closet about 50 feet away makes loud pulsing sounds in the pipes -- until I turn the toilet off at the wall again. The toilet flushes fine.

Defective ball cock or fill valve.
Tell us which one you have

Do you know how to adjust your tank level? Do you need instructions? Back to you, Tom

No, but with instructions I probably could do it. Worth a try to see if that would solve it. Thanks very much for your offer.

It looks like the second black and white picture. There is a white part called korky anti-siphon 523. Sorry I can't be more helpful.

Easy adjustment! For a Fluid Master ballcock you can adjust the level by squeezing the steel piece on vertical wire arm at the side, pulling the can up and down down. Pull the can up to raise the tank level and down to lower it. Set the tank level at 1/2" beneath the top of the white overflow tube. Good luck, Tom