I was under the impression that some electrics and hybrids in electric mode played simulated engine noise through speakers to both alert nearby pedestrians that

I was under the impression that some electrics and hybrids in electric mode played simulated engine noise through speakers to both alert nearby pedestrians that the vehicle is moving and to reassure the driver that it is operating normally. I wouldn't put it past a manufacturer or aftermarket parts maker to play "vroom vroom" noises over the sound system at speeds too low for the driver to actually hear anything from the passenger compartment. If you can put an aluminum spoiler on a stock Honda Civic, you can put an engine noise simulator on your sound system.