Originally Posted by AaronP
There are a number of reasons why the GPU might not be able to drop to the lowest performance level, including just needing enough memory bandwidth to display the screen. You could try running at a lower screen resolution (not that I'm promising that it will help).
Yes, thanks for the tip, that was it. When using the notebook without the external display, power management works as it should, completely noiseless. A bit sad, but maybe I*can try switching off the internal screen to keep the noise down. And now, to my next adventures with hdmi and sound ;-)...