Cadillac Repair: Whirring noise from behind instrument panel, cadillac sls, digital speedometer

Question
'00 Cadillac SLS 130,000 miles.  There is a whirring noise coming from behind the instrument panel.  Speedometer etc are working fine.  The noise has no particular pattern.  Sometimes it will keep going from start to stop of a long or short trip, sometimes it doesn't start up at all, and sometimes it will start and stop during a trip.  Has been like this for about the last 10 to 15,000 miles.

Answer
If you have an ANALOG speedometer (old style needle type) the cable needs to be removed from the backside of the instrument panel and lubricated.

If you have a DIGITAL speedometer does the noise increase and decrease with engine speed or is it a fixed speed noise ?.