2006 E55 with 113k. On way home the other day I noticed a loud shreeking squeal that lasted several seconds upon hard acceleration. It only does it in drive and when I mash the petal. It doesnt do it in park or when accelerating normal. First thought was sc belt or clutch pak. Replaced belt and checked all pullies which seemed fine...noise still there....used stop squeal on the clutch pak....still there....any ideas????

maybe your belt tensioner is going and causing your new belt to slip?

What Toad said..
Check both belt tensioners, since the noise you described sounds like belt slippage.