I really like that video Jennifer. My iEXOS-100 has always made that hissing sound from the control area and I wondered if it was normal, now I see it is. I haven't noticed that drastic of a change between firmware but I have always heard the pulsing sound when it is tracking. When doing high magnification planetary and Lunar imaging you can actually see the pulses in the movement of the image as it tracks, they time perfectly with the pulses heard from the control boards.
Unlike a constant spin of a servo motor, the stepper motors move in pulses, it is why there is no need for encoders, since the software knows how far the mount moves with each pulse. At low f ratio you won't see it, but when working at f10-f30 for planetary they are easily seen. Fortunately stacking software nulls them out and doesn't affect the image at all.
Dawson Springs, Ky
Scopes: Meade ETX90RA(deforked now) Sky Watcher 150MCT
Camera: ZWO ASI 120MC-S
Software: Explore Stars Android, ASCOM, Stellarium Scope, Stellarium, AS!3, SharpCap, RegiStax6.