what would make a humming sound only the passenger side and only at high speeds

Whereas the struts upper mounting bushings are a known issue with the Aveo , see technical bulletins for your vehicle, the actual cause of a humming will never be said items. Knocking,squeaking,groaning are possible , humming would be a different noise. So I am not sure if the disconnect is the description or the dealer technician. I agree these are all similar shades of a not well designed car.