I have a dilemma. I've bought 3 new cassettes. 2 SRAM pc990's and 1 XTR. I have a brand new 991 chain on the bike. Now every time I pedal there feels like there is a small amount of grinding going on. It's not audible or noticeable in the stand, only when riding. I know it's not the bottom bracket, or free-hub because it doesn't happen on a slightly older, but non-worn cassette I have. Any ideas?!