[CO Hummer]

I've had the Gobi rack on my roof for almost 4 years and haven't once heard it bang against the roof. Many time's I've been offroad with the tire on too (Stock BFG). While there isn't a lot of clearance, they designed it to stay rigid enought to not touch.

I'm not saying you don't have this problem, but if so I'd contact Gobi. Paul or Sandra will take care of you.

Here's an old picture of my clearance.