So I recently replaced my 9-speed Shimano 105 chain/cassette with a 6500 cassette and a KMC X9 chain. I re-mounted the shifter cable and dialed in the shifting. Everything is silent and works great except the 6th cog (from the top) in the back. It makes a clicking sound, almost as if the chain is catching on the adjacent sprocket, once per wheel revolution. It doesn't appear to be load sensitive, and I can't feel much in the pedals. What's the deal? Is the cog (or the adjacent cog) bent? Will this quiet down as the cassette wears in?