I have a noise that started a couple months ago - it is kind of a thump thump thump - mostly heard (well, louder) from 2 of the 3 toilets. Does not happen all the time. When it is happening, if you flush one of the 2 toilets, it stops - for a while. When it is happening, all the water in the house pulses. When it is happening, inside the toilet tank, the small thin tube that goes from the float valve part to the overflow tube - the water is constantly pulsing.
We thought it was related to the sprinklers. Turned them off and it is still happening.

Help it is driving me nuts!

Where is water being used when the thumping starts? Do you have a pressure regulator on the main input line?

It starts without any water being used. It is going on right now and I have been at the computer for over an hour. If I turn on the water at any sink right now, it will be pulsing - and that is what the thump thump thump noise comes from. The toilet tank is pulsing too.

Oh and I don't know if we have a pressure regulator... how do I check?