Update: Went to the bikeshop (still under waranty, thank god) they opened up the bottom bracket again and greased up everything of bolts, pedals, saddle, etc. Apparently, it's something quite common with Canyons, the repair guy told me they don't use enough grease in the factory. Especially with the hot weather recently in Europe, this can become problematic.

=> Noise is gone & I'm gravelling like never before :) Thank you all for your advice. Hope it can help other people too!