I've got a nasty rattle in my truck, when coasting it sounds like a spun bearing. I know its not the rear diff (My first assumption) since its new. What kinda bearings are we dealing with in the t-case, just input and output?

Mine makes the same sound after installing twin-sticks. I didn't grind off the ear enough. I figured it would just wear off, instead of splitting the case apart again. Been a year, noise still there, but I know what it is and it's nothing damaging.

oh really
this started a few months after dual cases went in, so I just assumed the rear case (donor) was the culprit. What ear are you talking about?
I have let it go for almost a year, but i've got a drivetrain vibe now around 20-40km/h, I know its not the diff or rear axle so I figured the noisy t-case bearing is jsut getting worse.

what dual case adaptor did you use?

marlins, non-clocked

that would not be it then,
I have an AA that made that sound since new.
going to replace it with marlins.

It was one of the shift forks. I bought a used transfer case, with fresh Marlin 4.7's for $220 - SCORE! It was a forward shift case. My truck is top shift. The used Marlin loaded case included top-shift conversion parts. I was able to do a direct transfer case swap, without opening my old stock case for any reason. It's the shift fork from the "conversion" that isn't ground down quite enough.
On a different matter, I LOVE the 4.7's. However, I really do miss the stock 2.88 low gear for cruising the trails. Now I really see why guys go duel cases, but instead of double low, I think (for now) I would use 2.88 alot more than the 4.7 doubled. All I need is the adapter, that's why I kept my old case, sitting in the garage cabinet.