My son, who is a Dell Ectric/electronic engineer, just popped in.
he reckons
Cheap. Unplug the speakers - small hope!
Try and roll back the video card drivers, or update (you have tried that, as you say in your post). He is convinced on this one, as he states the resolution on the taskbar is different from the rest of the screen.
Try changing the resolution, and see if there is a difference.
And, wild one, if you have a 2 pin mains adapter, turn it around!
Expensive. You may be looking for a different graphics card, but play with the graphics card control panel settings first.