I hate a rattling bike. My carbon synapse has been making a lot of noise on anything but smooth roads and those are few and far between around here. The bike has an internal cable for the rear brake and I thought it might be that. I've tried to apply brake to tighten the cable and see if that solves it but no change. I'm wondering what else it might be. One thought is the cables that run along the head tube and could be slapping there. I have checked bottle cages and it's not that.

Anyway have a similar issue and how did you solve it (if you did)?