I've got a older 4 cylinder (mitsu) that has 159,000 miles, I've tried both 10W-30 and 10W-40, the valves make some noise at start up and then quiet down after driving, is there a particular weight that might help? I'ved tried both the 40W seems to cause more noise to me. The manual says I can use 10W-30,40 and 20W-50.