NHTSA recently updated the rules for vehicle pedestrian warning sounds, and now allows user-selectable sounds. Previously these were prohibited, so vehicles could only have one fixed sound.

I'm not sure that "coconut noises" would be allowed, however, as the rules require continuous tones (modulated according to speed and acceleration) that must be recognisable as an engine noise.

Perhaps the coconut noise will be a manually-activated alert/horn feature rather than the mandatory pedestrian warning sound.