B5 S4 steering noise

[Ti Kan]

Hi everyone,

Patient: 2001.5 Audi S4 biturbo, 135K mi.

Symptom: Turning the steering wheel clockwise produces a groan/squeal
noise, it sounds like something needs lubrication.  No noise when
turning counter-clockwise.

This video shows the problem:
https://www.youtube.com/watch?v=LwDh4ddz7Pk

Ignore the clicking noise in the video, it's just me trying to turn
the wheel and hold the camera at the same time.

The noise occurs with and without the engine running, and with the car
moving or stopped.  It isn't very loud, despite seeming that way in
the video (the camera mic is very sensitive).  Music from the stereo
or road noise at >25mph will mask it.

I first suspected the clockspring, but after removing the airbag and
steering wheel, turning the clockspring by hand was smooth and noise-free.
I reinstalled the steering wheel and airbag.

What else should I look at?  I know there is a U-joint at the
bottom of the column near where it connects to the steering rack,
could that U-joint need lubing?  Looks like it would require
a contortionist to work there...  Could the steering rack itself
be the problem?

-Ti