This noise just recently started.. it's like a vibrating noise that comes from the back like the exhaust or something.. once i start hitting like 40mph or higher the noise starts coming up and the whole car shakes!! I have no clue what it is! what can it be? please help.. thank you!!

 

Sounds like a failing u-joint on the drive shaft to me. Symptoms sound identical to what I have experienced when a u-joint goes bad.