1997 Blazer 2dr 4x4 3-Button (2hi, 4lo, 4hi)

Here's the scenario:
Okay, say I take off fast and get up to speed I will hear this kind of buzzing sound after I let off the accelerator. As I slow down it turns into a loud roaring and grinding noise and when I stop completely it goes away with a popping noise.

4hi will not engage but 4lo does engage and does not make the noise period in 4lo.

If I ease around and not take off quickly it doesn't happen. If I take off moderately it will.

While driving, if I hear the noise and put the tranny into N there is no change. If I'm driving and here the noise it only happens when I am deccelerating. If I give it gas it goes away.

The other night it was making the noise as I was slowing down and I hit a bump and it popped and stopped.

It seems to be coming mostly from the front.

Any ideas?

 

So I tested the vacuum line at the actuator under the battery and there was vacuum even though it was in 2hi. If my research is correct, this means the vacuum switch on the transfer case has gone bad.

I did some test runs with the vacuum line pulled off of the actuator and it did not make the noise at all.

 

was that the final issue, im having something similar on my suburban.