09 Pathfinder squeaks like a my neighbors bed frame

2009 Nissan Pathfinder SE 4 banger 2WD. I have a squeak coming from underneath my car that sounds like a squeaky bed when you…well, you get the point. The squeak started about two weeks about, and only happened when I was backing it up. (Please hold your snickering to a low roar) Now things have progressed to where I hear it going forwards too. The squeak gets faster with speed but goes away at about 25mph. I have found that I only hear the squeak while the car is in gear. If I throw it in neutral and push it forwards and backwards, it sounds perfectly healthy.

Obviously this must be related to the drive train, and from research on the worlds most reliable resource, the internet, I believe it might be a bad U-Joint. However, the tricky part is this; When I took it to the shop and went down into the pit and listened to/watched the drive shaft as a mechanic drove the car back and forth, the squeak seems to come from the middle of the drive shaft…or as Nissan says, the propeller shaft. This pathfinder has a solid, one piece shaft that is about 5 feet in length. The squeak seems to come from about 2 feet from the rear of this shaft. The drive shaft seems to be a hollow aluminum tube.

Bottom Line question is: Do I have a bad U-Joint that resonates its sound into the drive shaft, or could the drive shaft be disintegrating from the inside
?