I've just driven my Fiesta at 90-140km/h. I'm not sure which "electrical whine" you're referring to... but I can hear soft whistling sound when I let go the accelerator (when travelling at 110+ km/h). The pitch gets lower as the speed decrease.
I feel that this isnt the sound you're hearing since you said that the pitch and volume of your Fiesta's "whine" dont change.
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