So, i've seen this on a couple of them. Sometimes when you rev these trucks it sounds like a beast and you can feel the truck rock. Other times it sounds like someone put a dampener on the exhaust and took it out of almost a "sport mode".
Im thinking it maybe the DISA changing up the intake sometimes at idle?
Has anyone else notice this?

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2001 X5 3.0i
2007 X5 4.8i