My setup is 32x18 with a Rennen Rollenlager tensioner on my old hardtail frame. I'm using the tensioner in push up mode, and taking up as much chain slack as possible for maximum wrap around the cog. I noticed when lubing the chain that as I rotate the cranks, there is one spot in the rotation where it "sticks" slightly, always in the same place relative to the crankarms. I took the chain off and spun the cranks -- no sticking, so I figure it's not the bottom bracket bearings. I'm thinking that maybe the chainring or the cog are not absolutely perfectly round, so if the chain is overtensioned it's possible to hit a point in the rotation where the chain is just a hair too tight. I think I'll try backing off the tensioner slightly and see if it smooths out.

Any other ideas? It's not noticeable while pedalling, but I'd like to know the cause.