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In the US it’s actually a Federal requirement that all EVs and Hybrids produce some level of warning sound up to 30 kph/18.6 mph: https://www.federalregister.gov/documents/2018/02/26/2018-03721/federal-motor-vehicle-safety-standard-no-141-minimum-sound-requirements-for-hybrid-and-electric
I work with a number of visually-impaired individuals and they’ve explained that what they hear from motor vehicles is, first and foremost, tire noise. With ICE vehicles the majority of engine noise is emitted from the rear of the vehicle, as exhaust: My VI friends say that they can tell if a car is ICE or EV only as it passes.
Plus, as all ICEs make more-or-less the same sound, people can identify that sound as “engine noise”. With every EV making its own synthesized sound – and all of those sounds being different – it will be difficult for people to determine just what they’re hearing.