GM mechanics 05 Chevy makin noise

[Lumber_Jack]

ok, got a 2005 z71 5.3 l.

There is a noise coming from underneath the console. Sounds like a chirping/sweeping noise that seems in synce with the turning of the wheels. It gets louder in 4hi, and louder yet in 4lo. My first inclination was U joints on front drive shaft. took it to auto repair in Oak Ridge, said U joints were fine, I said to replace them anyhow (170,000 mi) He said that was definitely not my problem. Frustrated I asked him why he though that, he said they look fine.

My thoughts and questions

1) in 05 does the front drive shaft still turn when in 2wd? it is an early 2005 model. I believe that it does, from the transfer case friction, not the front differential

2) if the shaft does not turn, do the gears in transfer case still turn? could the noise be a bearing the transfer case

3) what else could it be? the mechanice was going to replace the front wheel bearings, rear diff fluid, all this stuff and I know the noise is not coming from either end, but directly under the seats

any info or thoughts would be appreciated

[Caster]

Maybe a loose nut behind the wheel?

[Lumber_Jack]

Maybe a loose nut behind the wheel?

highly likely, but I dont chirp like that

[Lumber_Jack]

hmm, replaced U joints, still making noise. I think its the transfer case. ....unfortunately

[Lumber_Jack]

No thought from anyone?