So here i am. Just pedaling away and then boom, my pedal catches really hard,makes a popping noise, and then my chain is either really loose or just falls off the back and the tire rubs on the frame. I have a Haro Downtown. I try and make my chain tighter, same thing happens. Looser? same thing happens. I dont know whats going on and its really annoying because it does this every time. Please help me.