1998 Blazer Transfer case

I'm in the Northeast and we had about 6 inches of snow the other day. I wasnt going out that day, so I shoveled the driveway and moved my truck out of the way. I put it in 4WD to move it down the driveway and
back up, when I was done. I may have left it in 4WD over night in 15 degree ( F ) weather. This morning on drive to work 2WD, fine. 15 mins on the road, I take an exit off the highway and the Transfer Case starts making an awful rumbling / rapping. The noise is directly proportional to how fast I am going. Switching to 4 HI or 4 Low and the noise goes away. It is 2WD that makes the noise. I wonder if this has to do with TSB 99-06-04-056 [ Transfer Case - Binding or Shuddering ]. I put a call into a dealership to get some more info on this TSB. Was wondering if anyone had a similiar experience or could tell me about the TSB in general.
thanks
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Follow up:
Before I left work last night, same problem. This morning, ride to work, no sounds. Could it have been some kind of snow / ice got inside and froze stuff up? Maybe just some moisture inside? Any thoughts on anything?
-peter
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