schnitzelboy

The car is a '96 Quattro with manual transmission. This problem seems to have started up when I replaced the center bearing in the driveshaft. When the car is cold, when I rev up past 4k there's a loud buzzing sound from somewhere under the radio/climate-control cluster. It's worst at 4700 RPM, especially when decelerating. It goes away when the car gets warm. I've lived with it for years now, so I know it's nothing seriously wrong, but I'm trying to sell the car and it doesn't make a very good initial impression. Any idea as to what might cause a noise like this?

Thanks