Why do it make a knockin sound every time step on the gass
Possible low octain fuel, may want to try a tank of premium gas, or if the knock is low in the engine, then a rod bearing starting to go.
Bad rod, broken piston though these tend to make noise all the time, carbon build up on a piston, blown headgasket between two cylinders.
Possibly valve problems in your cylinder head or maybe loose or worn rod and main bearings, although your water pump on that model can also produce loud noise if failing.
Check for low oil. Harmonic balancers will knock as well when they are going bad.This is on the crankshaft pulley on the bottom of the engine.
Looking for a Used Grand Prix in your area?
CarGurus has 2,807 nationwide Grand Prix listings starting at $1,995.
Search Pontiac Grand Prix Questions
Pontiac Grand Prix Experts