This has been a problem on the whole GM line for a long time. For a while there was a lubrication procedure they were using on the steering intermediate shaft, but it did not help much. There is a technical service bulleting issued by GM that covers your problem, with a replacement shaft.
This bulletin is being revised to update the repair procedure with a permanent fix. Please discard Corporate Bulletin Number 00-02-35-003L (Section 02 -- Steering).
Some customers may comment on a clunk-type noise coming from under the hood that also can be felt in the steering wheel. These conditions may be more noticeable when turning at low speeds on rough road surfaces.
Use the information below to help diagnose the source of the noise.
DON'T DO THIS
Replace the I-Shaft with P/N 19153614.
Do NOT lubricate or exercise the I-Shaft.
Replace the steering column upper intermediate shaft with an improved design shaft that will eliminate the clunk noise using the procedure listed below.
Notice: On the 2002 and later model year vehicles, the steering column LOCK was removed from the steering column. It is critical that the J 42640 - Steering column Anti-Rotation Pin is used when servicing steering columns on 2002 and later model year vehicles. Failure to use the J 42640 may result in damage to the SIR coil.
Tighten Tighten the bolt to 47 N·m (35 lb ft).
Tighten Tighten the bolt to 50 N·m (37 lb ft).
Tighten Tighten the nuts to 20 N·m (15 lb ft).
Shaft - Upper Intermediate Steering