Do you hear the noise if you listen with headphones plugged into the headphone jack?
If so, then the display is somehow corrupting the audio. If you get a clean signal with headphones, but noise on line-out or from the headphone jack when connecting to some other system, then the issue is probably a ground loop problem. These are very different types of problems, even though the noise can sound very similar, so the first step is to try to figure out which type of problem you have.