If it's in the seat it could be the rear wheels/suspension, if it's in the steering wheel it's often the front. It could be wind buffeting if it's only when the windows are open. Bushings=possible, struts=not fast vibrations like a wheel vibration.
I just replaced a bent/loose tensioner stud and it made a noticeable difference in vibrations. These weren't whole car vibrations but more like a resonance. It was causing a misaligned TB so you might want to pop off the cover and take a look.
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