Hey dude, got a mechanic question. Trying to help a friend figure out what's wrong with a bike. Once per revolution of the cranks, it feels like someone is smacking the rear wheel. It does it with or without weight on the bike, the bottom bracket was my friend's first thought, but it seems fine to me. My first thought was hub, but could it be something with the chain/cog? FYI: Stock Fuji Track Classic, around 500 miles, original everything.