I just installed a new XT rear derailleur on my 1990 Fisher Paragon. I tuned it per Shimano's specs. Shifts well until I get to the middle of the 7 speed cassette. From there up, as the chain moves up to the 24, 29, 34 there's a little clicking, like the chain's just kissing the next cog uphill from it. I turned the pedal slowly and noticed a few rivets lightly brushing the cog uphill from where the chain sits. The chain is a SRAM PC51 which is about a year old, riding about 6-12 miles a week offroad. Is it common for the rivets to brush the cassette? I'm sure it's tuned correctly. There's no prob on the higher gears. Maybe just buy a new chain? It's the same chain I had on there before but there was no noise with the old derailleur which was really sloppy in its mounting bushing area. Thanks.