[DieselJJ]

What/where's the knuckle? Noticed the same noise on mine tonight. Took a ride on a creeper underneath while my wife idled up the driveway (yeah, I trust her and it's coming from where the driveshaft exits the transmission. The rubber boot is dry rotting and squeeking at low rpms........ Is this a failed seal and what does it take to replace?

That boot should just be a dust cover, unless its throwing oil all over your under side then I wouldn't worry, take a dab of grease and swipe it around in there if you can.