Joined: Apr 2012
Location: Jacksonville Beach
You're not using garbage brand gas are you? Here in Jacksonville, FL and surrounding areas, Gate stations are notorious for their poor quality gas. If you're not already using high quality gas, try switching to top tier (Chevron, Texaco, Shell et al.) for a while and see.
Also, why are you using 89 octane? This engine is made for 87 and it doesn't help to run 89 without a tune. If you have knock with 87, get a dealer tech to ride along and hear it so you don't waste your time and come out with them saying "we couldn't replicate the problem".
2012 V6 M6 Performance Package