I replaced the belt on. I replaced the belt on my Dirt Devil Featherlite Bagless Vacuum and the

Question

I replaced the belt on my Dirt Devil Featherlite Bagless Vacuum and the brush roller rubs and makes a very loud noise when turned on. I have gone exactly by the manual instructions and made sure the belt and end caps were on correctly, but the bristles still rub the back and it makes a very loud noise. Without the brush roller in the vacuum, it sounds and runs normal. What could the problem be?