Now I know what it is.
The starter motor has sprockets that turns the engine during startup. Many of our Subes have sprikets that donít engage fully therefore loosing or chipping away bits of the teeth in each startup.
Eventually when there are no teeth left, you will hear a whirr... thats it.
So in order to avoid getting stranded in the mountains where there are no garages, I would advise to have the starter motor pulled out and inspected.