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98 Jeep Grand Cherokee Transfer case noise

I bought a 1998 Jeep zj for $900 with a bad transfer case. I’m new to this car repair stuff, but I thought I’d take a crack at it.
I bought a used 242 transfer case (originally had a 249 with what I guess to have the typically broken viscous coupler) and stuck it in. I also cut the output shaft of the 242 case about 1.5 inches shorter (to match the 249 output shaft length).
The problem: As soon as I reach 35mph, the car makes a whirring noise of some sort that doesn’t go away until the car slows down to 2-3mph or if I put the car in neutral. Does it sound like the driveshaft or did I get a bad tcase?
I’ve taken out the front driveshaft to isolate the problem, but it persists with or without it there.
Here’s a video of it running on stands.