Identifying the fluctuation in the AoA signal as electrical noise does not make sense to me.
Being only present on the ground it is much more likely it is some form of imbalance situation in the AoA vane.
Normally you want the AoA vane combined with the internal rotating parts of the sensor to be balanced so it doesn't react too much to bumps in the runway or turbulence in the air.
So i find a mechanical problem with the AoA vane like a broken off part combined with a bend much more likely.
Also no one has explained so far why electrical noise would never be visible during flight.