2002 Ford Taurus Impressive Shaking at Higher Speeds

My car shakes noticably, especially at higher speeds - to the point where, if someone is talking, it sounds like they are speaking into a table fan! Not good. Taking the car up to 60 mph or above increases the shaking considerably and I'm starting to wonder if something significant underneath is getting ready to break and/or fall off. I had both ball bearings in the front replaced within the past year to 2 years. The front tires are relatively new and the back tires had a tread of 5, last time I checked (about 2 months ago). What would you suggest?

Thanks for taking the time to reply to my question - I really appreciate it.