Ok, so I dont know if I'm being stupid here or what, but I cant figure this out. Been assembling my new bike, running some IRD cranks, surly cog, and a Wipperman chain - all 1/8. When I'm spinning the bike, the chain will "jump" at random points. Chain tension seems fine and everything is tightened (lockring, cog), and this is a problem I have never had before. Dont wanna take it out on serious rides until I have this problem fixed.. any thoughts?