Signature A6 just turned 226k. Original turbos. Shop has reminded me of a slight turbo oil leak since 160k. Driving back from NY to MI last Sunday, weather +/-9 of zero. At exactly 2900 rpm I noticed a dentist drill whine from the center console area. Below, no noise. As I increased speed and rpm, it got louder. Several times I tried speeding up and at 3200 rpm (~80 mph) it stopped and did not re-occur when I dropped back down to 70-72. Then, a little while later it repeated. I have driven the car once around town and there was no whining noise at city speeds. Thoughts from those unlucky enough to lose a turbo??