Had new fluidmaster fill valve put in to fix a leaky toilet, and now there's a loud banging noise in the pipes (that was never there before) and not only after the toilet is flushed, it's pretty much intermittent throughout the day. Can't sleep at night... Help!

Sounds like you have two problems not one.

First you have a leaking flush valve or flapper. This is causing the toilet tank to periodically refill. Replace the flapper.

Your air chambers of shock absorbers have become water logged. Turn the water to the house off at the main valve. Open all of your faucets and flush all toilets. This will drain all of the water out of the pipes and let some air in. I like to let the system sit like this for a couple hours just in case any water is being held in the air chambers by a vacuum. Close all faucets and open the main shut off valve.