I got the extended varanty on my 09 Tahoe
I had to pay the $100 diagnose fee

here is the description from my invoice what had to be replaced:

Steering Gear seals on spool Valve binding up and causing the squeak noise when turning
Replace steering gear, fill. Bleed, and E2000 .7 to adjust Toe in setting and roadtest to verify repair.

The steering gear is the part under your hood where the lower steering column is attached to.

 

Lucky enough I have the extended warrenty

The Cadlic Dealer where I bought my 09 Tahoe Z71 replaced the
STEERING GEAR
Reason: Steering Gear seals on spool valve are binding and causing the squeak noise when turning.
Work order text:
Inspect and replaced steering gear, fill, bleed, and E2000 .7 to adjust Toe in setting and roadtest to verify repair.

So far I do not hear any more noise.

 

I had the same issue on my 09 Chevy Tahoe Z71
Here is the description of what had to be repaired from my invoice.
I'm lucky I got the extended warrenty
The Steering Gear had to be replaced
Why:
Steering gear Seals on Spool Valve are binding up and causing the squeak noise when turning.
Instruction:
Inspect and replace steering gear, fill, bleed and E2000 .7 to adjust Toe in setting and roadtet to verify repair.

So far I do not have this ugly noise anymore.