When I purchased my Envoy five months ago, the used car dealer just changed the oil (not sure what he used) and used an AcDelco oil filter. Now, the oil life monitor shows it has 36% left and has a total of 152,000 miles on it. The engine has a cold knock that goes away when it warms up and I want to try Mobil 1 oil to see if it makes the cold knock go away. That being said, I'm not sure what kind of Mobil 1 oil to use. I saw the regular Mobil 1, High Mileage, and extended performance oil. Since the Envoy has over 75,000 miles, I would assume I should use the High Mileage oil. Is this correct? I have read that I want to use a Mobil 1 oil filter, correct? Thanks for the input!