My wife's 2007 BMW 535xi. It has 158,000 miles and when we go over 60 mph, we hear whining vibration. She took it to a mechanic, but the mehanic says that it's nothing wrong.
You went to the wrong mechanic. It’s whining and it is not supposed to whine. A good mechanic can analyze it. This could’ve been beyond their knowledge or they don’t know much about BMW. Watch my video, "how to find sources of noise in your car." Get it all set up, put it in your car, set up four different transmitters, the receiver and headphones, and when you drive it you can pinpoint where the whine is coming from. On BMWs, a lot of times, the whining would be wheel bearings on those things. Wheel bearings are notorious for going out. A worse case would be the transmission bearings wearing out. You’ll want to figure this out soon to prevent any further damage. I would recommend having a mechanic, such as one from YourMechanic, diagnose your car’s whining noise to determine exactly which component is faulty.