I bought a 2003 GMC Envoy 3 years ago and it has 240k miles on it now. It has been a very well kept vehicle. I have had no issues with it except for the quiet engine knock that it has. It's prominent when its cold but goes away at higher RPM and after running for a while its nearly silent. Any ideas what it is? Oil changed every 3k miles, has the 4.2L I6 not the V8.
Try switching to Premium and see if it goes away. Its likely that the engine is wore but hopefully the high test fuel fixes it if not you might have bigger problems underlying and I would take it to a mechanic you trust to run some tests if it gets worse
I have tried 89 gas and it doesn't seem to change. I don't think it's rod knock because it goes away after higher rpm and after driving a while.