http://www.youtube.com/watch?v=Wz0FFZdSCmo

I feel like it's not supposed to make this sound. I noticed a slight whirr while riding last night and figured it wasn't good... The hubs/chain/cog are all like 5 days old, still lubed up and fresh. What could it be? The chainline looks straight... Each tooth is catching right in the middle of the chain.