Having experienced and solved the maddening clicking sound several times: Does it click when you stand up out of the saddle? If not, it's likely your seatpost/saddle. Remove and clean seatpost and clamp. Add a smidgen (microns, as said by morneS555 above) of carbon grease on the section that goes into the seatstay. Re-assemble and test. If yes, it could possible be a dry rear (through) axle. Take out the axle, clean it, and apply just a smidge of grease. Re-assemble and test. Good luck.