[cdog]

Are you sure the headers are tight to the head and the exhaust is tight to the headers? I've had mine loose and it causes nasty backfires. That could be the source of all your noises.

If you want to pull the valve covers, you can visually inspect the rocker arms and pushrods. If a valve is messed up, you'll likely see a rocker arm thats also messed up or not holding it's pushrod.