Not bad at all but I hear the typical Golf GTI sound between the main soundwave like I'm used to hear from my X5M. And that's not a joke but even crappy. A good customer of mine bought a new X5 4.8i and I won't believe it how well it sounded compared to the X5M.
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Kind regards, Conny 

Porsche 997.2 Turbo S  *  BMW X5 M