2002 Mazda Protege 5 high speed steering wheel vibration

I have a 2002 Mazda Protege 5 that when driving around 120km/ph there is a vibration that is felt through the steering wheel. It starts out strong and slowly diminishes but then comes back and repeats the same cycle. My garage did a wheel balance and the problem is still there. There's nothing felt at low speeds, does anyone have any experience with this sort of scenario??

Thanks.