Last time out on my CAAD 5, I was annoyed by a slight rattle coming from the bike on rough stretches of road - i.e. a lot of the time, given our local road surfaces!
It took some tracking down. It turned out to be the RH brake lever which was slightly loose. Campagnolo brake levers do not have return springs - they rely on the tension in the brake cable to pull them shut when the lever is released after braking. There was enough friction in the cable to stop that working properly. I turned the bike upside down and squirted some thin lube down inside the brake outer. I then repeatedly operated the lever to work the lube down inside the cable. It helped, but it didn't entirely fix the problem.
The 'proper' solution would be to replace the brake outer cable (and probably the inner while I was at it) but I didn't want to have to take my nice new bar tape off to do that. (I know I could reuse the tape but it took me 3 attempts to get it neat last time!)
I came up with a work-around ... I normally release the brake lever slowly like this - LET GOOOOOOOOOOOOOOOOOO. That gives friction a perfect opportunity to stop the cable sliding back inside the outer. If instead I just do it abruptly like this - LET GO - the brake lever snaps back to its correct position immediately; 100% effective at stopping the rattle!
I'll put a new front brake cable on next time I change the bar tape.