I have a 99 Seville STS. I'm trying to get rid of the valve rapping noise at startup. The noise comes immediately then goes away after about 3 or 4 seconds...sometimes sounds like a diesel truck! I've only had the car about 6 months. I've tried adding Lucas oil stabilizer but I'm not sure it helped at all. I'm using Quaker State 10-30. Do I need a lower viscosity? Remember it's hot here in GA.