Ok so... I was driving my Blazer to work and it bucked lightly but noticeably on my a couple of times almost felt as if the 4x4 was trying to engage. It has done this to me a couple of times and has happened after about 30-40 minutes of interstate travel. When slowing down to get off of the interstate, this loud semi high pitched buzzing/grinding noise started coming from the front of truck. Freaked me out. When I was pulling over to hopefully keep from damaging anything further, it stopped.
While in park I eased on the gas a little and then little more to see if it would do it again... It didn't.
I proceeded on cautiously and the noise didn't happen again and the tranny shifted fine with no issues.
​​​​​Since then it has happened 6 more times, always when slowing down foot completely off of the gas. When it happens it seems to occur when decelerating from at least 50mph. The noise lasts for about 5-7 seconds, transmission shifts fine and otherwise runs well. I thought it may have been the 4x4 being partially engaged, but upon checking today found that the line going to the 4x4 actuator has been disconnected and capped off. This thing has really become a labor of love/hate. Thanks in advance

 

Anybody?

 

It's hard to say. Mine, for example, right after cranking a cold engine in park position makes a 2-3 second long of "ring-ding-ding" while hunting the idle setpoint from down below. Then, once it warms up, the noise is gone. I've made over a 1k miles with such a phenomenon waiting for an obvious damage to carry on, and still didn't figure out what that is. It still "ring-ding-dings" the same as it was before. Maybe one day I'll make an audio record to spare

 

unhook the vacuum lines from the transfer case switch and see if it doesn't happen again..If it doesn't, I would replace the transfer case switch...