What can I do to stop my front dérailleur rubbing against the crank arm?
If you already adjusted the front derailleur, there is not much to do. As you wrote yourself, the distance between crank arm and chainring is too small for your derailleur. Ask Rotor about compatible derailleurs.

The main reason to have derailleur not touch is not noise. The derailleur scratches the crank, which creates a starting point for cracks.