The rear brake rotor isn't supposed to be loose, is it? When I took off my rear wheel to change the tire I noticed that the brake rotor rattles. I tried to tighten the screws and they wouldn't budge. I tried to loosen them and they still wouldn't budge! I think the previous owner got really hamfisted with the bike since I've found a few parts that are way tighter than they should be a couple with red locktite on them when they should have had blue. To tell the truth I've been running with the loose rotor for a long time but didn't think anything wrong with it since it was like that when I bought the bike a couple years ago and didn't know any better.