The problem is we have over the years got to recognise the sound, I stopped in Spain trying to work out who was talking to me, and nearly got run over, as a wagons reversing beeper instead of beep beep beep was saying in Spanish beware I am reversing, had a sales man try to sell me one in the UK, but when the boss asked how it knew if to speak Welsh or English he had no answer, beep beep beep is far better universal language. As to hiss hiss hiss, that's daft, too many items make white noise.
As to the push bike or in my case e-Bike again a problem, ring ones bell and people jump, in my case blowing the horn people don't expect bikes to have horns, and be it a bike about to pass a pedestrian or a car passing a bike, to ring bell or blow horn just before passing is likely to make people jump and cause rather than guard against an accident.
Although there is quite a winding noise from my motor on the e-bike, people tend not to hear it, saying good afternoon as one approaches seems better than a bell or horn, blowing the horn is seen as being aggressive.
The main problem with the e-bike is the anti-motorcycle bars on cycle tracks means I can't have mirrors as then bike will not fit through the bars, any mirror less than my body width I can't see past my own body, these
effectively stop cyclists having mirrors. Even pedestrians have problems
and they don't stop motor bikes anyway, so rather pointless. However until banned there is a problem
Sustrans does give assess sizes, and at 1250 mm width I could have handle bar mirrors, however there is a second problem for me, getting my bike on the train, even when bike bends in the middle I can't get the bike into the carriages except for the special adapted disabled carriage. And even on the veranda to close gates on the carriage I need to fold the bike, so again a problem if I fit handle bar mirrors. So sound is the only way to know when some thing is behind one.