I have a 2006 BMW 525i that is experiencing a very noticeable vibration from the speed band of about 55-70 mph. I am not sure what is causing it but I have after market eibach performance springs and after market wheels. My suspension guy says that since it only occurs at certain springs that it is either the wheels and tires or something in the drive train. I just hat the wheels rebalanced and rotated today and it did not seem to help. Any ideas?