Thumping in the pipes when I flush toilets

For some reason my pipes have suddenly started thumping when I flush my toilets. The thumping seems to be coming from the location where the main enters the basement. I thought maybe the vacuum breaker on the sprinkler system was bad, which is directly adjacent to the where the main comes into the house, but the thumping continues even after I close the sectional valve that controls the lawn sprinklers which is upstream of the vacuum breaker. the pressure in the system has not increased (city water). Any thoughts \ tips | or suggestions on localizing the issue would be appreciated. Thank you.

Check out this video from "This Old House"
https://youtu.be/3-Bhr2IKIF8

It's likely because the vent pipe for the sewer gases is loose and not secured.

The water hammer may be coming from the installed prv. Do they go bad? How can I test it?