When upstairs tub valve is opened for the first time in the evening, loud banging noise sometimes ensues from pipes. Banging is alleviated when supply is redirected to showerhead, or when water is turned off.

Single-handle Pegasus (Home Depot) valve. No issues when supply is off (not "water hammer").

Appreciate any feedback. More specifics available if needed. Thanks.

When I said "supply," I meant the tub valve itself. Not the main, though I will try that. No issues when water isn't running.

Only an issue with the tub valve which gets used once an evening. No problem when switched to shower (stops banging).

Old house. Fair water pressure at best (well, jet pump). Highest point in the house. Water is slightly acidic, so I do get deposits.

Thanks for your feedback.

Shut the water off to the valve and open it up. Look for anything loose in the valve body. Now turn the water back on to flush out the supply lines. Reassemble and test. Good luck, Tom