Guys I left the car for a week and since I've started it again (and put a new BM53 in) it makes a sound when the engine revs. It sounds a bit like a static sound from the radio, sort of a background noise, so much so that I even turned the radio off to make sure it wasn't coming through the speakers. It's not though. I have no idea if it's important, I completely understand that it's hard to diagnose without more info but I really don't know what more I can say.

__________________
2005 X5 4.4i Sport Sterling/Black