I recently felt what I thought was chain skipping once in awhile. After checking the chain, there was 1/16 of wear. I replaced the chain and then it started jumping/skipping all the time in gears 15 and 17 regardless of the pressure on the chain. After lifting up the bike and turning the pedal, the derailer was making a clicking noise. After making an adjustment to the cable on the derailer, the derailer stopped clicking, but the problem moved up to gears 19 and 21. Besides the chain being new, all the components have about 3000 miles and the cassette appears to have sharp edges and not round ones. Any suggestions?