Man you picked the wrong time of year to buy a used X5, the cold weather seems to magnify everything thing that's wrong with the X5, good luck tracking down the noise.

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2002 X5 4.6is
1999 C5 Corvette
1992 Mitsubishi 3000GT VR-4
1994 Kawasaki ZX-9R
2005 Mazda 6 Wagon (Wife's)
1991 Mitsubishi 3000GT VR-4