ok so when I pedal and get to a certain rotation on the cranks the back cog like pops loud. it's not the chain not lining up, i thought it was the chain its self. well i take it in, and the guy says the chains practically brand new. and I was like well what else could it be? he said he had no clue, also mentioned the cogs should be replaced soon but that was not what was causing it. I said like 15 times when you RIDEthe bike it makes the sound. so what does he do? he puts it in the stand and spins the pedals. and after 5 min says he cant hear anything. now I have nothing against the man, he is nice. anyways, when you have pressure on the pedals it pops and only when. you can spin the wheels for days and nothing will make a peep but once you sit on the bike and ride it, it sounds like it's backfiring. any clue what it is? i still think its the chain. i think a link is stiff and when the pedals get to that certain point the cranks pull the chain tight and the chain snaps back into straight giving the cog slack for like a millisecond before it gets tight again and makes that poping sound by pulling the cog back to tension if that makes sense.