I just switched my 99 2.5L Duratec to Pennzoil HM 5w-20. When I get on the highway and accelerate quickly to 2500 to 3000 rpm, I can now hear valve clatter. I've got 150,000 miles and have always used 5w-30 until now. I think I'm going back to 5w-30. Anyone else have this problem?