One problem related to gas tank strap has been reported for the 2007 BMW 328. The most recently reported issues are listed below.
Sound of metal being dragged along the ground. Friends wired the metal piece to car's underbody and I drove over 300 miles on the highways not realizing it was the strap for the gas tank. Took it to BMW and they were unable to get it on a lift to diagnose the problem, due to time constraints. Took it to local mechanic and he put it on the lift and took off the the 'broken' strap. Now waiting for two days for the piece to come from BMW. Went online and saw there were other postings on a BMW 'blog site' referring to this problem, and causing me some alarm that the gas tank could split!!! hope this isn't a problem with a lot of 328xi models!.