1999 Pontiac Bonneville Vibration

1999 Pontiac Bonneville with 86,000 miles has vibration in seat, and little in steering wheel. Slight vibration at 50 mph, very noticeable at 70 mph. Vibration becomes worst and then gets better, then worst, at any given speed. Tires have been balanced twice. I switched tires with known good set - vibration basically stayed with car. There is a small cut in rubber boot of right 1/2 shaft. At 30 MPH, you can hear a noise in front that I thought was tires at each rotation. Now I think it may be front wheel bearing or half shaft.

Have you ever heard of a bearing causing a vibration?

Is there a likely cause of the vibration?

Any diagnostic I can do rather than just change parts?

Thanks,
Ed