Originally Posted by sivat
The chain, chainring and cog were all brand new. It was a wipperman 152 chain, and vuelta chainring. My problem sounds exactly like what 11.4 described. Its possible that, with a different chain, the problem wouldn't have occurred.
EDIT: Actually, rereading 11.4's post, that wasn't quite the problem I had. The problem that i had was the tooth profile on the cog had a ridge that would catch on the ends of the narrow links of the chain when the tooth was in the wide link. this would lift the chain until the tension built up, the snap the chain back onto the cog. It was worse when I put backpressure on the chain. I blame gravity for that.
I had a similar problem with a NEW Izumi chain and a USED Surly cog (both 1/8")....I assumed that it was because the cog was worn. It turns out that that the Surly cog is worn, but I got it to work semi-smoothly with a new KMC chain. However, it is just utterly incompatable with the Izumi chain and it made horrible rough grinding noises very similar to what you are describing.