Quick question?

Hi,I just got my 99 sport a couple of days ago. When I took the jeep out for a test drive I did not here this noise but while going home on the parkway avg. 80 mph I here this noise from the rear end area and a slight vibe. the jeep only has 43K ion it.can someone point me in the right direction at were to start looking. tried search but could not find anything.

A quick question with no quick answer. Tires usually vibrate around 60 MPH or so, underline around. I´ve had 80 MPH vibrations before, due to front axle shaft U-joint wear. Rear driveline vibrations often go away or change depending on the cargo load (GVW). Had a vibration that drove me nuts, turned out to be the roof rack. Good luck and good hunting.