Does my 400ex need carrier/wheel bearings?

it sounds like carrier bearings. keep your chain adjusted slightly tighter than usual. you can run it some with it that way. stay out of the mud! if you're going for a looong trail ride, you should replace them. also know that if you let them go too long it gets real expensive when you eat into that carrier housing!!! i've ridden many miles on bad bearings, you just have to watch them close and run a bit easier than normal. if at all possible change them before your ride, other wise go easy, have fun!!