The radio antenna is part of the rear defroster in the rear window.I believe the radio antenna is in the slanted far-rear window on the passenger-side.
It sounds like your belts in your tires may be starting to separate. My mustang started to shake at highway speed. New tires cured it. My 05 Pacifica still rolls smooth. No problems so far
The jack for a 2004 Pacifica is located under the storage compartment in the back of the rear most seats. Open the storage compartment lid, then lift out the storage tray.