i just got back from a lengthy (read "dirty") bike trip last weekend. While cleaning my bike I wanted to make sure things were mechanically ok. My hubs have this "gritty" kind of feel and sound when i hold them by the hub and spin them. they don't seem to have any trouble spinning forever though. Also, my cassette has a little "wobble" in it. is this normal? or is this a problem that can be easily fixed a la me?