There is a GM TSB (superseded several times) which addresses this issue. I have access to the latest TSBs (which apply to my '04 Silverado) via my ALLDATADIY.COM subscription, but I hesitate to post the entire thing here. At any rate, here's how it begins:
Steering - Underhood Clunk Heard/Felt in Steering Wheel
Bulletin No.: 00-02-35-003N
Date: March 26 2008
Clunking Noise Under Hood and Can Be Felt in Steering Wheel and/or Steering Column (Replace Upper Intermediate Steering Shaft [I-Shaft] Assembly)
2002-2006 Cadillac Escalade Models
1999-2007 Chevrolet Silverado Models (Classic)
2000-2006 Chevrolet Suburban, Tahoe Models
2002-2006 Chevrolet Avalanche
1999-2007 GMC Sierra Models (Classic)
2000-2006 GMC Yukon, Yukon XL Models
2003-2006 HUMMER H2
This Service Bulletin DOES NOT include Mid-Size Utilities such as Buick Rainier, Chevrolet TrailBlazer Models, GMC Envoy Models or Oldsmobile Bravada. Refer to Service Bulletin 02-02-35-006A or newer for Mid-Size Utilities.
This bulletin is being revised to add diagnostic information (refer to Diagnostic Tips) to check the lower steering column bearing as a potential source of the noise. Please discard Corporate Bulletin Number 00-02-35-003M (Section 02-Steering).
The entire TSB, including a step-by-step procedure, requisite precautions and tools
, and detailed images, is posted (by a FORMER GM Parts and Service Mngr, named Mike) at the following link... I suggest a SAVE TO DISK complete with ALL IMAGES, once this page loads: