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?

If you are sure it's once per wheel revolution then logically it has to be something on the cog itself - some kind of defect, such as a burr.

It's definitely not related to pedal position or pedal revolutions, as it speeds up when I get into the big ring regardless of how fast I'm spinning the pedals.

I'll take a good look at it...

see if you can identify the teeth involved - you may have a burr as was noted above, or possibly a bent tooth

i'd expect it to be a simple filing exercise, or maybe some gentle bending required and you'll be back to silent running

I don't know. I can't see anything.

Maybe include a picture.

Josh