No grinding noise here. It's just faint humming noise that wasn't there a few weeks ago. Last time i heard a similar noise was on my E39 M5 and it turned out to the those rubber grommets that hold the oil filter housing and power steering housing to the chassis of the car. They were deteriorated and the housings were rubbing up against the vehicle causing this harmonic noise. I'll check those out because it could very well be the same thing!

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2004 BMW M3 Individual
2009 BMW E70 X5 35d
2011 BMW E70 X5 35d - Totaled
2009 BMW M3 E90 - SOLD
2006 E53 X5 4.8iS - SOLD
2002 E46 M3 Convertible - SOLD
2006 E46 M3 ZCP - SOLD
2011 E70 X5 35d - SOLD
2000 E39 ///M5 - SOLD
2003 E53 X5 4.6iS - SOLD
2006 E83 X3 3.0i MSport - SOLD
2000 E46 323Ci - SOLD