Chain grinding on lower-gear of rear cassette
I recently bout a new wheel, 8-speed cassette, and chain. The cassette is a HG-50 (RSX) 13-26 and a HG-91 chain.
When I ride on my rollers, I notice a horrible vibration and grinding sound when in the 15 tooth and physically smaller gears (13 & 14). It is silky smooth in all of the other physically bigger gears (17 - 26). It is the same regardless if the front is on the 39 or 52.
As far as I can tell, this is due to the chain rubbing on the physically larger gear of the cassette, but I'm not 100% certain this is the case. This cassette has never been taken apart.
Also, when I ride on the road, I don't notice it at all. So, I suppose it's not as bad as I made it out to be. I'm sure it's still there, but all of the other vibrations and such mask it.
Any ideas to track this down?