06 Tahoe LT: Groaning Noise = Traction Control Problem

[lukesisme]

Vehicle:
2006 Chevy Tahoe LT 4x4 w/ 5.3L V8. 86k miles, everything is stock, and I don't think any major systems had previously been repaired/replaced.

The Noise:
My truck frequently exhibits a groaning noise when accelerating away from a stop. The noise seems to originate below the dash and slightly to the left of the driver. Opening the driver-side window/door does *not* increase the apparent volume of the noise.

Other Symptoms
The noise is paired with varying degrees of power loss and, perhaps 20% of the time, a 'Traction Active' message. Manually disengaging traction control/stability using the traction control switch generally prevents the noise/power loss from occurring. Could the noise I'm hearing be the the Transfer Case Shift Motor?

The noise always ends before the transmission shifts to 2nd (it peters out prior to the shift, rather than ending abruptly at the shift) Again this is with stabialtrac enabled - default setting on startup. Turn it off, all works great and no whir/grinding heard.

Error Messages & DTCs
In the past I had occasionally received a 'Service Stability' message on the dash (and, I *think* a 'Service Traction' message, but I may be mis-remembering). I had also occasionally received a 'Service 4WD' message and replacing the selector switch fixed that. For the last six months I've been driving with traction control switched off and none of these messages have appeared.


Analysis
It seems obvious the issue is related in some fashion to traction control.

Any ideas?