Buzzing luggage rack on westy need advice

Anybody know a surefire way to keep the luggage rack from "buzzing"?

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On�our very first trip in our 90 Multivan this happened and we were freaked out. It was loud!� When you stick your arm out and touch the rack you can feel it buzz.
Pulled over to the side of the road and�applied a strip of black tape across the gap of the luggage�rack. "3-M weather resistant tape, 1 inch",� It lasted as long as�we had it--8 years. Fit right in with the windshield gasket and no one ever noticed it. 5 minutes and about 50 cents worth of tape.
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About a half hour later we filled up with gas for the first time and noticed gas leaking� somewhere from the tank, That was freak out #2. Welcome to the Vanagon. Within a couple months we had most things sorted out.
Chris C