how many miles does the truck have its probaly your timeing chain puting higher octane gass is only makeing a bigger boom than the rattle its slef with the engine shut off not started if you do this with the engine started you will lose a finger open the oil cap use your finger to find the timing chain and gear try moveing the chain real fast if the chain moves replace it or don't it'll go about 160,000 miles before breacking or longer