My wife's Cannondale Synapse mixes a KMC chain with 105 3x10 derailleurs and a Sram cluster. She's got ghost shifting issues and general noise from the RD, both of which I can confirm from riding with her. On the stand I can't duplicate the ghost shifting, but the noise I can. I've tweaked and adjusted and even given dirty looks, but I just can't settle the thing down to be as quiet as my 7800-equipped bike.
It looks like the noise comes from the chain juuuust catching on an adjacent tooth of the next-larger sprocket, and then uncatching. It's most prominent in the smallest sprockets, especially when in the middle ring.
On a hunch, I measured the KMC chain, and compared it to new Shimano and Sram chains; the KMC measures ~6.1mm, while the others are 5.95mm (assuming I remember how to read a vernier caliper right). Dunno if that matters, and I think I recall that Shimano's spec is 6.1, but it's interesting nonetheless.
So, ideas? Anyone think a new Sram chain would help?