Transfer case

I recently developed a grinding noise that start at slow speed and get louder thru the high speed (squeling high pitch nasty). today I lifted the rear and put in in gear and found it coming from the transfer case. Qiute nasty. i have 217000 miles on it and never dumped the fluid. While it was up and spinning I could hold and stop the front driveshaft and it still made the noise.
My questions are
1 is this typical noise
2 How do I identify the case for a new one.
3 Is this a tough job.
4 Will a case from a 1998 Yukon match up to mine (locally available, what is that worth)
5 how soon till it goes (work transportation.
I know it is a lot to ask for but you guys helped out before and got the jobs done.
Thanks
Jim

?1. Not a typical noise.
?2. Tags at the rear of the t-case.
?3. Depends on your skill level and tool chest.
?4. Hard to say since we don't know what you're working on (year, model, etc.)
?5. Since it just started, probably not long.

Sorry I forgot, 1999 tahoe 4X4 4 door
Thanks

Really need to identify the one in your '99 and the one out of the '98.

Basically GMC & Chevy used GM t-cases. But there are different GM t-cases used depending on model year. (auto t-case vs standard t-case).