1996 Ford Bronco Body Shaking at High Speeds

The Bronco runs fine, except that at higher speeds, the entire body starts to vibrate.

It continues even when you take your foot off the gas pedal and does not stop until the vehicle is below 50 mph.

Otherwise, there are no problems with acceleration, etc.

Also, the right side of the engine lifters are once again, EXTREMELYloud. It almost drowns out the sound of the Flowmaster muffler (smile - this is only a joke, it's not quite that bad). Do you have any recommendations that I can implement or do I need to consult a professional mechanic (again)?

Thanks!