I've run into a n annoying issue with my Campy Centaur derailleur and chain. Over the winter I did a complete bike overhaul and all parts were stripped and cleaned, adjusted and lubed. But now I noticed a problem (i.e. noise in the rear). Namely, I adjusted the derailleur according to Campy specs and it shifts flawlessly. However on two (sometimes three) gears the chain gets very noisy. In the 3rd and 4th smallest cog the chain makes noise but in all other cogs it's quiet. I tried multiple times to readjust the whole thing but to no avail. I am now at the point of buying a new chain but I still think that the chain is fine. Does anyone have any ideas what could be going on here?