Reply To: Loud thumping noise in wall after toilet has filled

[nicktheplumberParticipant]

Your symptoms are classic for WATERHAMMER, which is a loud banging sound when a fixture valve closes. It’s usually associated with faucets, but don’t forget that the ballcock valve in your toilet tank is a valve just like any other.

You could try doing what RP suggests, or you could install a water hammer arrestor on the line to the tank.

NtP