Sometimes it will almost sound like valve rattle at higher RPM's. I was having that symptom in my car. Replaced the MAF, and htat helped, but the main cause turned out to be dirty injectors, and spark plugs gapped at .35"!! I found I can still get it if I romp it hard w/ A/C on.

I put my first tank of premium in last week, and it seems to help. I'm going back to regular this week and see if I can tell a difference. Wondering if mid-grade would work...

I think I'm all stock.