We installed a Harbor Breeze Cheshire Fan and our problem is that when the fan spins the blades hit the cover making quite a loud noise. We have tightened the blades and have checked all screws, its all mounted properly but cannot figure out what is wrong. Please help

I had a similar problem with a ceiling fan that stumped me for a while. After checking everything I finally found that one of the screws inside the housing was too tight and caused the outer housing to bow just enough to make contact with the blades. Everything else about the install looked fine and I didn't see the bowing until I got high enough on the ladder so that the fan was at eye level.