I also had what sounded like valve noise during light acceleration. It seemed to get worse the closer to a regen it got. I had to bring the truck in to the dealer for a bad battery, and had them do an oil change( first one) while there. On my way home after picking it up, I noticed on my paperwork that they put 6 quarts of 5w30 dexos in my truck. Turned around and went strait back to the dealer and told them they put in the wrong oil. Dealer looked up my vin on their computer, and 5w30 dexos was listed as the correct oil. I showed them the manual, and the oil cap on the truck shows 0w20 dexosD. Dealer called GM, and it was determined that the info in the computer was wrong.(How the he** does that happen). After another oil and filter change with the correct oil, no more valve clatter!! Maybe the oil that was originally in there was wrong also?