Loud vibrations in water main after water heater replacement.

So we got a new water heater today (+ the expansion tank that wasn’t there b4). After trying to drain the air out of the system, we still have this new problem of pound vibration/shuddering noise from the water main anytime a faucet is turned on. Except if I turn on multiple faucets & the shower head on the top floor. Then the whole thing stops. Which leads me to believe it’s more than just some air trapped in the system.

The expansion tank says it’s preset to 50 PSI and I had an emergency plumber come out with a gauge to read the water pressure of the main at 45. I did that while the HVAC guys who were installing the heater were still there. Even the plumber was a little stumped because his original guess was that the PRV had gone out. But after taking the pressure reading and looking at the actual valve, he said that looked all good (the valve itself looked fairly new). He then said it could be air in the system somewhere and might take a while to fully air out. Then he left.

Now I am sitting here worried because this is another thing on the long list of things I have to navigate as a new homeowner, kinda feeling a bit hopeless. Any time I turn on the kitchen faucet, I can hear the loud vibrations. What should I do in this case? Should I give it a few days or call another plumber?