Help - Clicking, then Hum, Transfer Case?

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Feb 3, 2006
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I was going up a steep hill in Duluth, Mn yesterday and heard some clickingwhen accelerating at low, city speeds on my '03 GMC Sierra with 163,000 miles. Not the original transfer case fluid. The clicking went away after several miles for the most part. Then, a resonant hum started around the location of the feet between 60-65 MPH. Everything looks fine under the truck. If I go faster than 65 MPH, the hum goes away! I pushed the 4x4 selector switch to "Auto 4x4" and back to "2 HI" and heard no difference. It seems like it is stuck in "Auto 4x4", but the hum is louder. I drove 3 hours with no issues, but the hum is still there and had plans to tow a 3,000 Lb. boat today. Should I? Any idea what this problem is? Should I just change the fluid or bring it in? Thanks!
 
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Nov 22, 2004
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The clicking and hum sounds are classic symptoms of a U-joint going bad. Check your rear axle drive shaft and see if you have any play (best to jack up truck w/tires off ground). Visually look at the U-joints for any wear. Doubtful it's in the front but do check your fluid levels in both axles and transfer case. Did you use the correct fluid in the t-case?
 

Turk

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Yep, used GM Trac II 50k ago. Its probably a u-joint. Odd the transfer case switching makes no difference though.
 
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 Originally Posted By: tpitcher
Yep, used GM Trac II 50k ago. Its probably a u-joint. Odd the transfer case switching makes no difference though.
No, it's not odd if it's the rear driveshaft U-joint because that one is always in use.
 

Turk

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As a follow up: The front U-joint was the culprit. Replaced the rear one at the same time today. Problem solved!
 
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