I have had quite a loud knocking sound coming from my girlfriends rear wheel which speeds up and slows down as the wheel rotates faster and slower. It started to turn into a grinding kind of sound and became noticeable louder so the insides of the hub were replaced but the old hub casing was left the same. The same knocking sound was immediately apparent as I left the store so I am back to square one. Anyone have any idea's please as I am clueless and the shop I got the bike from seems pretty unknowledgeable also. Thanks.