" I fear in your case the PTU for some reason is not allowing for enough speed difference between front and rear axles in the turns or to account for pressure that can build up from small differences in axle speeds while operating in 4wd. It is not enough to cause binding just complaining in the form of noise. This also will increase wear on certain driveline components this could account for the metal shavings. I have seen these types of things on part time 4wd systems that were run on high traction surfaces by people that had no clue they should not do this. I have even seen u-joints that blew out and ring and pinion gears break teeth in extreme conditions."
Chris, this is what is so frustrating. The new PTU had only 1400 miles on it before the techs found the metal shavings in it. It starting groaning at about 100 miles after replacement. The tech told me over the phone how disheartening it was to see the metal shavings in the unit. As we speak the thing is still groaning and vibrating. What a shame as my wife's 2014 Jeep Cherokee is quite and has had no issues what so ever. That was one of the reason I went with the Compass in the first place.
I had a few minutes to goof off and see what I could find relating to your problem. Not only to see if I could help you and others but I also like to be aware of any issues I might see at some point. As you can guess there simply is not much out there for our 2nd gen Compass they are just too new and not enough of them on the road with many miles on them. However the Compass sister vehicle the Renegade has been around a bit longer. Many of these share our complete drivetrain and chassis so a bit of searching under those yielded the thread below on another forum and it warrants reading all the way through as there are references to a PTU software update when available. There are also some tips that might help you determine if your issue relates like shifting to 4wd when you hear the noise to see if it stops. If nothing else if your issue is the same you know if it is that common of an issue.
Grinding/vibration/rumble Noise at ~30mph - Jeep Renegade Forum