The distinctive sound of the Harley v-twin engine chug is important enough that Harley Davidson applied to the US Patent Office in 1994 for a patent on that sound. Nine competing motorcycle brands opposed their application and after six years Harley withdrew it.
Seems to me that distinctive chug sound should easily pass the legal test of an intellectual property right....go figure!
Somewhere in Germany, there must be a BMW bike with straight pipes and no mufflers, too?