2007 Jeep Commander Bad Driveshaft or ?

Looking at a 2007 Jeep Commander that’s equipped with Quadra drive 2, and I test drove it and seriously considing buying it but theres one big issue with it, if you go under 20 MPHS you can hear from the back seat area something grinding and spinning and other odd sounds. But once you go past 20 it disappears. It drives fine and shifts good. Only other thing is the brakes make a loud scape like noise once you completely come to a stop, As if they were wet.
I am unsure about this issues would appreciate any help.