... and that's the hum of an internal combustion engine.
The attempt to make electric cars sound like ICEs is silly. First, it's motivated by people attempting to use their guts to determine what constitutes a safety feature. It's all very intuitive to think that a noisy car is safer. Except that it really isn't. Pedestrians don't rely heavily on their sense of sound to avoid getting hit. They just don't. Spend time watching pedestrians at an intersection, and you'll realize that they're either (a) not paying attention at all, or (b) using their sight to avoid cars.
Trying to use sound to avoid collisions is problematic for two reasons. First, because all the other cars in the vicinity that don't pose an immediate threat are also making noise, the noise of cars closer to you gets drowned out. Second, because it's very hard to tell where a sound is coming from, especially in urban environments, where sounds reflect off buildings. Do the experiment yourself. Close your eyes, and listen for cars, and see if you can tell where they are. It's extremely difficult.
Electric cars also are not silent to start off with. They still produce wind noise, and tire noise, like other cars.
But, perhaps the biggest logical farce is that these noisemakers are being justified based on a multi-year study done by NHTSA, whereby hybrids got into a higher number of accidents with pedestrians than conventional cars, and at low speeds, hybrids work similarly to electric cars (can be quieter). The factor by which hybrids got into more ped accidents was about 1.4 (40% more). That's not a huge amount more, but it certainly is noticeable.
The problem is that the study did not account for the environment hybrids tend to operate in. With half of this country living in urban vs. rural settings, you don't see hybrids represented equally in both. By a two to one ratio, you see more hybrids among city dwellers. And if you look at overall pedestrian accident data, you'll see that pedestrian accidents are twice as likely in urban environments. So, the increased rate of ped accidents with hybrids can probably be explained completely by simply understanding that they operate in riskier environments.
The study also only attempts to address accidents caused by the car making the noise (or not). The study makes no attempt to understand that aside from the car that actually hits the pedestrian, every other car in the vicinity was making noise that made it harder for that particular car to be heard. Electric cars make the environment quieter for everybody, which could have a small beneficial effect that makes it less likely for all the cars around them to go unnoticed, because of ambient noise. In game theory terms, this is a true Prisoner's Dilemma, where the automakers are concluding that every car should be noisy, in an attempt to out-noisy the rest, paying no attention to the net effect of all the noise pollution.
When you consider these factors, you realize that the overall affect on pedestrian safety from quiet cars is very small. Certainly nowhere near the 40% figure that's spawned this hysteria.
This is really just an attempt by the auto industry, that is really looking for excuses to say, "we just can't build cars competitively any other way ... and thus were right all along to populate the planet with pollution machines". It's pretty pathetic, really.