There is going to be some noise in 4wd at speed but I cannot say if
yours is excessive without hearing it. The "clunk" was because
synchronize in Tcase is likely getting worn and not smoothly bringing
front drive shaft up to speed to engage it. Realistically, shifts in to
4wd should be made a a lower speed because it is easier to get drive
shaft up to proper speed to engage it. (20MPH or less)

On 1/27/2009 10:35 PM, wrote:
> Is it possible to 'spring' a transfer case? I was heading out of town
> on ran into black ice as the freeway started up hill. There was quite
> a bit of traffic and I started to fishtail on the Interstate at about
> 35 MPH. I didn't check the speedometer but guess I was around 30 MPG
> when I pressed the 4H on my 1997 GMC Suburban to engage the four wheel
> drive and heard a fairly loud CLANK.
>
> So far everything is, and has been working fine, but for some reason
> at around 50 MPH, I hear a kind of loud whining that either sounds
> like tire noise OR my transfer case. I wonder about this 'sprung'
> transfer case thing because years ago, a friend had an old Ford 4x4
> pickup that howled pretty badly at highway speeds and he told me that
> he had 'sprung' his transfer case (never said how he did it, though
> his would have been of the year where you had to be at a complete
> stop).
>
> I was under the impression that with the push button to engage 4x4 GM
> products, a person could be rolling down the road at 30 MPH (or so)
> and be okay doing this. I guess in retrospect, I'm still glad I did
> it because I think it kept me out of a winter nights freeway collision
> but am a little concerned about the howling sound (again, kind of a
> loud road noise sound).
>
> Anyone else experienced this or have ideas?
>
> thanks,
> John