Hi. The car has developed a soft whirring that is strictly road speed related.
ie: it doesn't change tone or pitch with steering, engine revs or brakes.

If i was in an older holden, I'd swear it was the speedo cable. However, the Mk3 is all electronic and the speedo is as smooth and sweet as new.

The whirring drops out at 20klms or below (doesn't fade - just ceases).
Above 20klm it starts as a lower tone and increases to a higher frequency the faster we drive. But it doesn't get louder, just higher. It is strictly in time with road speed. Its like a constant very low volume tone, with the occasional small amount of warbling just like a slightly noisy cable might sound.

Any ideas?