Order up one of these. Should fix all your problems.
Kensington Noise Reducing Car Audio AUX Cable
If you don't think it works there are some vids on u-tube before and after using it.
i had a 2002 envoy with the same motor, no matter what oil i ran in it for the first 5mins on a cold start it would knock. It's piston slap and GM says its normal. All most all 4.2 do it on a cold start up dont worry about it.