What’s the scraping/hissing sound when I drive slowly?
Q: What’s that sound when I start driving?
A: People variously report hearing a scraping, hissing or even sometimes a hum when they are driving slowly with a Zilla. This is perfectly normal for a Zilla powered EV and is not likely to be your driveshaft scraping on the body (though it could be that).
Due to speed limitations of high power electronic switching devices it is necessary to modify the pulse width modulation (PWM) of power devices in a way that has audio consequences. We could have made it squeal like some other controller manufacturers did, but decided that we found white noise more pleasant. This is a noise made by the motor in response to the spread spectrum frequency modulation that it receives while the Zilla is in current limit. Since it happens while in current limit and when the motor voltage is very low this sound is usually only heard when the motor is turning slowly. The speed range over which it makes the sound is more pronounced in both single ratio and high voltage vehicles.
-Otmar