I think I am having a similar problem, did it almost sound like there was an artificial engine/exhaust sound coming from behind the firewall. I'm pretty sure there was not active sound on 2007 x5 but I could imagine that it might sound similar (sarcasm). It almost sounds like I am playing a video game when driving (the sound that is). Going to probably take it to the stealer on monday, although I am out of warranty but have an extended warranty that covers most things.