Every inductive load under variable current generates spikes and will try to keep the current constant.
The way the inductive load do that is by creating an opositive voltage to what had created the initial current flow.
This voltage is high because the impedance is high and can damage electronics devices conected to it.
Interference is being trasmitted by air as electromagnetic waves and on the power suplly wires.

Don't believe it? Plug an osciloscope and watch!

Nilo