I'm not going to get into an argument about what nosier, but my 110" Harley with de-catted header pipes and 2.5" baffles barks with the best of them.
I have the factory Harman Kardon head unit but have upgraded to 7.25" front three way speakers with their 200w amp. At 80 mph I can hear my tunes just fine and my wife hears them from the back just fine....
One possible small difference: the wide open plains (and roads) of the Land of the Free, vs the smaller highly populated roads (and concentration of urban areas) in Europe. On US road trips I've sometimes been delighted to see another vehicle - in Europe I'd be amazed if I didn't see one (or pedestrian or cyclist). So music noise pollution is a potential issue...
