noise at rear left wheel only in reverse???

I'm hoping someone here has experienced something similar to give me a head start on what to look for...

When in reverse and going very slow, I can hear a rhythmic rub at the drivers side rear tire which increases with the tire rotation. When the speed increases enough, it seems to disappear, but may just be constantly rubbing and that noise might just be drowned out by the engine. I don't hear it when driving forward at the same speed. If I had to pin the sound down, I'd say it's almost like a warped rotor/brake pad rubbing kind of sound. If that were the case, I'd think I should hear it when driving forward...

Any theories?

Thanks :thumbsup: