How do I fix noisy pipes after a toilet fluch?

First: Turn off and back On your toilet supply valve. If noise still persists than remove fill valve and clean it. It is not making positive seal making the noise in process.

This could also be water hammer if you fill valve is snapping closed to quickly. You can add a Sioux water hammer arrestor or resupply the air chamber that is likely inside the wall but out of sight. SIOUX CHIEF 660-2 MINI-RESTER WATER HAMMER ARRESTER 1/2" To try resupplying the air close your main supply to the house, flush the toilet and then open the connections on the shut off valve under the tank near the floor, there will be a cup of water so catch it in a bowl. Allow this toilet supply line to drain for a few minutes and that should let air get back inside the chamber. Over several years that air supply can get absorbed/dissolved into the water and you cushion of air in the chamber is no longer sufficient.