I have a 2003 Envoy XL 5.3L V8 that has an annoying whistle at approximately 10% throttle and under. Is this a normal condition? I had checked around and already replaced the PCV valve as suggested by others, but that didn't solve the noise. It doesn't sound terrible, but is a little annoying. Another thing I've noticed is that the truck doesn't seem to sit level side to side. I'll try to get out and measure to see which side is high/low. I heard there might be a Service Bulletin for the dealer to fix this. Any truth to that? EDIT: They probably all have it, but ours is air ride in the rear.