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what is that noise?

> From gajewski@ug.cs.dal.ca Thu Feb 25 06:04:26 1993
> Subject: what is that noise?
> To: quattro@aries.East.Sun.COM (audi)
> Date: 	Thu, 25 Feb 1993 10:03:42 -0400
> X-Lines: 22
> Hi there,
> Our audi 90 developed some weird high pitched noise from the fan
> that heats the car. SO when the fan is off, there is no noise,
> when you put in in position I,II or III, the noise gets louder and
> higher pitched. Also noticed that it happens more in humid weather.
> Is there some kind of belt that can be slipping? Something needs to
> be lubricated? That fan seems to be working but that noise is just
> terrible.
> Thaks for any suggestions.
> ANdy

I had a similiar problem with my Audi and a domestic car.  The noise
was coming from the fan motor brushes rubbing on the motor commutator. 
My solution was to clean the commutator until it was shiny copper with a very
fine abrasive such as a piece of crocus cloth or an electrical contact
burnishing tool. A piece of worn emery cloth will substitute but do not use 
sandpaper and do not lubricate the commutator. I used a strip of crocus 
cloth held around the end of an ice cream stick.

Usually the commutator can be accessed through holes in the motor housing 
without taking the motor apart and having to wonder how to get the spring
loaded brushes back on the shaft.  Another less likely noise source could be
the motor shaft bushings needing lubrication. Of course the hard part is
getting to the motor :) Hope this helps.