I have ridden a bike and coasted at some speed. 35+ over rough pavement and smooth both asphalt and concrete. I have also coasted in a vehicle at high speeds. The large auto tires with a more aggressive tread and a large footprint make noise, the bike tires just make a hiss with a buzz from the freewheel. Of course vehicles with a very aggressive tread make a huge amount of road noise. Listen to one of those lifted trucks... I still think the major noise is chain noise having heard it first hand on my own bike, and machines without tires or engines, just motors. Unfortunately that noise represents an energy bleed. Has anyone ever used a belt drive for a high speed run? A belt makes a similar noise but much more subdued due to an elastomer impacting the sprocket rather than a hard steel ring.