I have also isolated a noise by taping a microphone to the parts in question and driving. It helps if you have a stereo recorder and can use 2 mics at the same time. One front and one back or one on the drive housing and one on the rear end. The wind noise is a problem and I just put some tape over the mic so you are just picking up the vibrations. Just a thought.

Neil
http://community.webshots.com/user/neilhatten