To: audi-20v I realize that this is anecdotal and unscientific, but FWIW, I just filled the case with Red Line 20W-50 and I'm getting more of that tap, tap, tap than usual. Usual has been Mobil 1 20w-50. I have put in Durablend once and the motor never ran quieter...I may go back and try that again on a regular basis. Just my experience, that is all. RoT