I have not tried it on the freeway yet.
I have noticed a low level humm at just over 60km with a slight vibration once over 80km. This is with the kargo master minus the basket and luggage bag, it sounds to me like noise is being created by air passing the front bar which i hope will improve once basket and bag are in place.
Plan B is to turn the radio up
I know a guy who can fabricate me an air deflector from stainless if it becomes a big problem.