Before you take this route, have you performed the Golf Tee mod on the exhaust flap? Google it for an E46. I ASSUME an E46 330 and your x5 have the similar exhaust/muffler system where the flap inside in the dual tip opens only at certain RPM ranges to allow more air flow/better meaner sound... You can look inside your dual tips and see if the flap exists and or is closed. If you open it fully manually and put a golf tee in the vacuum line then you will like the sound more. But don't forget it IS just a 6cyl and will not bark like a 8 cyl

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I swear, my cars are like a girlfriend.
Sometimes its a rough ride, sometimes its smooth motorin'.
Sometimes she doesnt like how i treat her and sometimes i dont like how she behaves.
BUT at the end of the day, she loves it when I am inside her.

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'91 850i
'05 X5 4.4i
'09 Clubman S