if you're running V-brakes, it's the spring tension of the brakes that's causing the rub. this happens to me (only on the front wheel) whenever i change my tire or take off the wheel...and i'm running xtr brakes..just make sure you carry a phillips head screwdriver w/ you and center the brakes when you put the wheel back on. (push down on the handlebars and wiggle the wheel to make sure it's totally in the drop outs). good luck bro