I've never heard eisenmann drone as long as it was run with the cats. I had the race system on my e92 m3 and while it really screamed when you got on it, it was never obnoxious. I'd figure that on the x5 it couldn't possibly be any louder than an m car.

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01 X5 3.0i (gone)
04 X5 4.8is (gone)
06 X5 4.4i (gone)
09 X5 35d (current)
12 X5 35d (current)