The amount of misinformation being disseminated about this problem in this thread is amazing.

There is a service bulletin that describes this very problem as an issue with wheel bearings and flanges on the front of the X5. The dealer has to install some new flanges and bearings and the popping sound will be rectified. Mine was done and the problem is gone. It's a multi-day event because of the time involved allowing the glue to dry. No Kidding!

The moment I mentioned the popping/clunking sound to my dealer, he explained the issues and the solution. Any dealer who doesn't know about this action is not paying attention to the service information being sent to them.