almost all slr's make a rattle noise when you shake it. Things like the mirrors are never hard fastened, because if they were, what would happen if you dropped it from a very low height? The mirror would shatter because there wouldn't be any "give". Having it just a little loose allows it some give. You likely just never noticed the rattle before hand. Of course, it could actually mean it's FUBAR.... but u never know. how much did the camera cost exactly? If a little piece if off kilter inside, it seriously shouldn't cost too much if you bring it to a respectable repair shop (look around for those "Mom n'Pop" type shops, they tend to be a little more honest and are more likely to give u a better deal). At the very least, get an estimate. If it's too much, get a new camera, and then also get a handheld light meter if you can afford one. Hand helds will give you , generally, a much more acurate reading than an in-camera light meter, and are much more useful for shyte like studio shoots, or ones where you have time to use a hand held.