Help with my suburban please

[Highway Star]

I've never had a big 4wd before. I understand a little about what happens to engage the front drive system, but obviously not enough.

Something is wrong, or bad, or wearing out, or about to let go in the drivetrain system of my '96 GMC Suburban. I don't know what it is...

I can hear and feel a vibration, I really think two parts that should be coupled or uncoupled are grinding on each other. The first time I heard this noise, I took off in the rain and the rear wheel started spinning. Then this awful grinding noise. It sounded like it was coming from the transmission. The sound changed pitch with wheel speed, not engine or trans speed. I got to a place where I could stop and at least give a visible inspection for something hanging down or out of wack. When I slowed to a stop, I heard a clunk and the grinding noise stopped. After driving some more, it felt like it went in and out of manual shift on the fly 4wd just fine.

Today, it happened again. Then when I came to a stop, I felt the same clunk and it stopped.


Have you guys ever heard of anything like this? I'm outta my league. Thanks.