Plumber installed new water heater. Toilet now sounds like a freight train after I flush it.

Please help me y'all. I just got a brand new water heater installed yesterday by a reputable plumbing company.

As soon as the plumbers left, I flushed the toilet in the adjacent bathroom, and a loud noise like a vibrating freight train happened for about 10 seconds. It now happens every time the toilet is flushed. The toilet is not hooked up to a hot water line.

I called my plumbing company, and they said it might be an issue with the toilet valve? But this was not happening AT ALL prior to the change of the water heater. In my mind there is no way this situation is not somehow related?

Please, can anyone explain why switching out a water heater would cause an intensely loud vibration sound coming from my toilet? Is there anything that could have caused that to happen in the process of switching out the water heater?