I have a 1999 Suburban K1500 that has been driving myself and my well meaning neighbors absolutely insane. The truck runs beautifully and has 120,000 miles.
Shortly after we bought an old boat, we noticed an intermittent rattle from the drive train area when the truck was under a load. It happened frequently when towing; but it would still happen if you accelerated at anything more then a moderate clip unloaded.
First thing we did was drain the fluid out of both the transfer case and differential looking for a clue. The transfer case fluid looked bright red; and the differential fluid was foul as all get out (in other words normal for being unchanged for who knows how long). Both me and a couple others dug around a bit and could find no signs of ware anywere inside the differential. Just for giggles we popped out the axels and replaced the rear bearings and seals and hoped for some luck. No chance.
I also had an intermittent misfire indication that came up. On the off chance that was causing some funky exhaust noises, I also swapped out plugs, wires, rotor and cap. Fixed the misfire light; but nothing for the rattle.
So, I have now given up two weekends and am hoping for a best guess for a third.
Honestly, I would swear the thing sounds like an intermittent chain slip (transfer case?) but a couple of my well meaning neighbors, well sticking their heads under the 6,500 lb four wheel drive while it was rocking back and fourth, really believe it is a possible U-Joint fault.
I did take it to the local mechanic who thought it may be exhaust related; but I’m not even sure he loaded it up enough to hear the sound.
Those vehicles made strange noises as the driveshaft yoke moved in and out of the transmission. Keeping it lubed cured it.
We talked about greasing the driveshaft; but I was under the impression you coudn’t grease this model? What exactly should I lube, and with what?
Ach! I answered the other post.
Anyway, the yoke (not funny eh?) oldschool mentioned extends from the tranny and with a u-joint attaches to the driveshaft. Some have an external grease fitting some don’t.
U-joints with no visible fitting SOMETIMES have the grease fitting hole plugged with a plastic cap which you remove and insert a grease fitting. For these all you need is a tube of grease and a grease gun. (not expensive)
(Todays U-joints are factory packed FOR LIFE according to GM.) These must be removed and replaced if worn out.
Is this a one piece or two piece driveshaft with a hanger bearing?
Sorry this took so long to post. Anyway, after everything I tried, I dropped the rear driveshaft and the rear u-joint was all but rusted into place. Brought it into town and for $80 they rebuilt both ends and whalla (spelling?).
Anyway, hate to bring this post to the top but I appreciate all the suggestions below.
Thanks for letting us know the final result.