Ok well heres the problem. The chain on my bike seems to tighten and get loose when the bike moves. Instead of like a regular bike where the chain stays the same tension it gets really tight and then loose. At first I thought it was the sprocket but it doesn't seem to be that off and is actually pretty centered. I don't know why it does this and it's really annoying because whenever I hit a certain speed the chain starts vibrating like crazy and makes a very loud sound and the bike won't budge any higher from that speed. Anyone know if this is a common problem or if anything else could be causing thing? Also the sprocket isn't 100% centered but it is extremely close. Any ideas?