I’ve had a similar experience to your coworkers’. I was walking along the road in a state park last summer and a Prius came up behind me. I didn’t even hear it until it was practically on top of me, and I didn’t realize it was a car until I turned around because it was only making a faint whining noise. I can definitely see why they’d be a danger to the blind community, although it’ll be interesting to see what sort of noise is added.