We live in a 3 year old house and when we flush any of the 3 toilets, there is now a continuing thumping noise that is coming from inside the water heater closet in the garage.
There is a water pressure adjuster screw in one of the copper water lines, and I tried to adjust it, however, either the water pressure would be way too low when I got the sound to stop or it would continue to thump when I got the water pressure adjusted to an adequate level. How can I stop this thumping noise? I would appreciate any and all help!

Thanks!

John