I have a 2000 model Oldsmobile Alero v6 and it sounds like it's knocking or something but when u pull a plug wire it stops. What could that be?

Answer: It is possible that there is a tear in the plug boot, so what you are hearing is the spark grounding itself to the side of the head and it goes away when you pull it out because it has no where else to ground to but itself. This will usually result in a tick, not really a knock. Also you would notice that the engine is running rough, hesitates on acceleration or even a check engine light with a misfire code stored.

Another possibility: If you mean that you were removing spark plug wires one at a time, and one of them caused the knock to stop, then that means that cylinder has a mechanical problem. Removing a plug wire from the cylinder that is knocking and the knock stops is a sign of worn rod bearing since the combustion and related pressures are eliminated when taking that plug wire off, thus no force on the piston to cause a worn rod bearing to knock.