I have a 2004 Jeep Gran Cherokee, 87000 miles, 6. I have this sound,sounds like the the lifters,but it goes away and comes back on ,goes away,comes back. My mechanic said it could be exhaust mantifold ,another says lifters. My main mechanic told me to change my oil to 20/50 and put in STP oil treatment. that did not work,then told me about another oil treatments? Please help!