4wd noise

[jeepstud]

Hello Guys-

 

2002 GMC Sierra SLE with Autotrac, 5.3L. Recently I have been having some new noises that sound to me like expensive noises. To aid troubleshooting I will try to provide as many details as possible.

 

The noise itself is somewhat of a rattling/ratcheting/tingy kinda noise. It does not sound or feel like something is binding then releasing (pop). It is not a growl (although mine does growl as well) Instead I guess it sound more like a baseball card in bicycle spokes, it is rythmic and seems to change frequency with speed. It is fairly loud, loud enough so that you could hear it if i rolled up next to you.

 

The noise does not occur in 2wd at all. The noise will occur in either Auto or in 4HI. I have not tried 4LO. As near as I can tell the 4WD appears to be working correctly. The auto kicks in smoothly and bites hard, as does the the 4HI. The noise only seems to occur as I coast down or maybe coast around a corner. As speed slows down it starting making that tinking noise. To me it sounds like it is coming from the drivers side (although that is where I am sitting).

 

I changed the front end oil and didnt see any chunks of metal and no change with the noise. I checked the 4WD actuator and moved in and out. I pushed on the fork the actuator moves and it felt free. I am not sure that I have ever heard CV joint noise although since the CV's spin all the time I would have expected to here the noise all the time (correct me if I am wrong). I did not see any burned out u joints on the front drive shaft and I could not get the CV's to make the noise on their own.

 

I put the truck up on a lift and could not repeat the noise. So it looks like it will only happen on pavement.

 

Is the front driveshaft a slip yoke style with a u joint in the front?

 

 

 

Any help or suggestions of things to check would be appreciated.

Thanks

Trent