After having my new aero handlebar installed I developed a cable rattle that sounded like it was emanating from inside the frame (internally routed cables – best thing since sliced bread btw).
After a few days, and a trip to the office in the back of my SUV, the rattle went away. I figured the trip jarred something in the right way (for once). A few days later it came back and I got lucky… Going over a train track I just happened to catch the two left cables rattle together out of the corner of my eye. The next day, I went up to the shop to see if there was an easier, more aesthetically pleasing, solution than electrician’s tape. This is what I was given:
2 seconds (not including the ten minute trip to the bike shop) and it would have cost less than a buck (had I paid for it – I did not).
Fit Recovery 
That’s one of the reasons I like Jagwire cable sets, they give you a few of those things in each package.