I just finished up a major upgrade on my Roubaix Comp during which I upgraded from an Ultegra 6503 triple to a Dura-Ace 7800 and I also upgraded its wheelset to a brand new set of Zipp 404s. The upgrade went very smooth and everything works great. Everything fits perfectly. It shifts nice and crisp. However, it now has a noisy drivetrain that I've been trying to nail down the source of for the last 24 hours.
The noise sounds like it is coming from the rear cassette and chain, and it seems at its worst with the bike in the 53t front sprocket. It starts when the cranks are spinning at a fairly high rate of speed, and right at that point when there's not a lot of load on the pedals. When there's a load on the pedals, it's quiet. It's just at that point where the crank is spinning with just enough load to keep up the speed, but not quite enough to increase it (sort of cruising, for lack of a better term, if that makes sense).
The sound is sort of a grinding rattle, and it does it to some degree across the entire range of gears.
I've checked and rechecked everything. I readjusted both derailleurs numerous times. I've checked and rechecked chain length numerous times. I followed the instructions when assembling. I've read Sheldon's site, Park Tools site, Zinn's book of bike repair, and Barnett's book of bicycle repair. I've searched BFN and googled this thing numerous times. Everything is brand new.