Earlier this week the plumber came to fix the toilets in our house. He did a minor rebuild on two of them (not sure this has anything to do with our problem, but it started as soon as the plumber left). While he was here, he measured the water pressure and told us it was 80psi (same as we'd been told in the past). So then the problem begins.

Now when you first turn on the water there is about 3-4 seconds of very high flow and then it cuts back. We tried adjusting the water pressure regulator, but that just makes the eventual flow less and does nothing about this initial surge. We measured the water pressure at the hose bib outside (supposedly where the plumber also checked) and it's now at about 120. Any ideas what this could be or even whether it's related to the very coincidental plumber visit? Thanks for any advice!

Sounds like you've had a PRV, (Pressure Regulator Valve) that's gone bad. Tha average house pressure runs between 40 and 50 PSI. At 80 PSI you were almost twice that and at 120 PSI you are off the scale. Too much pressure puts a strain on the joints in the piping and on the valves and faucets in the system. You have way too much house pressure. Have the PRV checked and if it's faulty have it replaced, Good luck, tom