Weird popping noise only in 4wd

[john2115]

I never post on here but I am always looking around. I bought a 2000 GMC Sierra Z71 about 3 months back, it was cheap I only paid 1k for it as kind of a project truck. So here is my issue, popping/ grinding noise from front end ONLY in 4wd and only when I give it some gas under 10 mph it is fine and no noise is present. Does not matter if I drive straight or turning it is present either way. I am stumped because when I google searched the symptoms I basically came up with a wide variety of possible issues from cv axles to transfer case chain stretched to even the front differential needing a complete rebuild. I am very mechanically inclined and have rebuilt axles, motors and transmissions before so I can do the work myself but I am stumped on the possible issue. This weekend I plan on pulling the front diff fluid and inspecting it and possibly pulling the whole diff out and apart to get an in depth look. Main thing I am asking is if someone has had this issue before because it could possibly be something small to where I don't need to pull it.

 

Since I bought the truck I have replaced all suspension and steering parts in the front end, only things I reused was knuckles and cv axles. This noise does not happen at all in 2wd and I hardly drive this truck at the moment anyways until it is 100% complete.

 

I plan on rebuilding both axles, transfer case, transmission and motor in the very near future but I am trying to diagnose this noise before I move on. Any help would be greatly appreciated or even a good way to help diagnose the noise.

[00Silverado4x4]

Get the whole truck up on a lift or jackstands and then put her in 4wd while running and then climb under to pin point where the noise is coming from. That way you're not guessing. That's what I'd do anyway.

[FBarber1]

2000 & 2001 models had an issue with the diff case being worn from the inside. I heard a similar noise in my '01 Chevy about 2 years ago. Ended up replacing the diff cover (was completely worn through) and rebuilding the front diff as well. Hope that you don't have the same issue, or it truly will be a project truck.

[john2115]

Yeah might try lifting it up to pinpoint it. Do the front diffs have a diff cover?

[00Silverado4x4]

No diff cover for the front.

[john2115]

That's what I thought.....couldn't get the sound to replicate on jack stands. I'm guessing it needs to be under load.

[john2115]

Found the sound it's coming from the transfer case....checked the fluid it's the original red from the factory. I know it's supposed to be blue now.

[02suburbanZ71]

Sounds like the tcase is toast

[FBarber1]

Excuse my brain fart, I dont know what in the hell I was thinking. I meant the transfer case. You are correct, there is no diff cover on the 01's

[FBarber1]

http://www.gm-trucks.com/forums/topic/48648-hole-in-my-transfer-case/

 

Above is a thread that was started on the problem a couple years ago. Hope this helps.