interference from a wiper motor - in which circuit did you tap to power the AEs (if they are aftermarket)?

if the AEs are stock, and you have the LEDs flickering, than it is a poor RF insulation and/or ground insulation. look into ground loop isolators for the ground feed of the LEDs.

for the RF insulation, consider aluminum grounded foil - they sell metal tape at home improvement stores (duct metal tape) that has sticky one side and can be wrapped around some wires in place of shielding... this definitely will look ghetto...