The noise came from the emergency gogwheel which was scraping against the regulator.
I managed to cut if off while in place, using a carpet knife. The base is still there but not touching anything.
The problem of the cogwheel was there when I assembled the parts. It was scraping against the regulator. I then filed it down to what I thought was small enough to clear the regulator.
Now I know more!
Anyway, I think that the rubber clutch is good enough to turn/assist if the electics fail. Often it is a question of getting off the "startline" before it takes off on its own.
These cars are very individual !!!!
You did not disclose whether you were referring to the front or rear windows.
If its any comfort to you, from time to time I have heard the same shrill sound from the right rear window. When that sound occurs, the motor is obviously turning but the window remains unmoved. (This seems different from your problem.)
Each time I removed the access panel to observe the mechanism with the sound, I was unable to find or duplicate the problem. I lubricated the motor, its gearing and the window track, but it did not seem to make any difference. The window would operate normally for weeks and then - without warning: "shriek." I have assumed something was stripped, but could never find any hard evidence of that.
Now that you mention rubber clutch, I remember strongly suspecting it changes with age and ambient conditions and it may occasionally slip and thereby create the offensive sound. I am not aware of a means of reconditioning the rubber anymore than I know how to recondition old tires without re-vulcanizing them. So, I have lived with the off and on problem.
FWIW.