I bought a cheap bike and a few days later I noticed the back wheel was slightly wobbly. I also hear a whooshing sound from the wheel rubbing against something but I can't locate where its coming from. I've turned the bike upside down and spun the wheel, I can hear it but there is no place where the wheel is actually touching something, its a real mystery. When I ride my bike I feel like I'm exerting a lot more energy than I should and the bike slows very quickly after I stop pedaling. What do you think the problem is, do you think it could be a result of the wobbly wheel alone?