Zed101

From your description, it appears that there is an open shield or ? on the power supply. Check for any wear and tear on all connectors, broken shields on the video inputs (probably most likely), Anywhere there is a connection that may have a shield. Also, your proximity of the tv and comp/powersupply may be too close. try moving it as far as you can from the tv. Use an estention cord if possible if your other leads are long enough. Just make sure ALL the connections are good and nothing frayed etc. You may also have a defective power supply for the laptop as it only occurs when it is being used with the external power supply. Even though it will still function properly for charging the battery, Your computer has extra filtering which may filter out the buzz which appears to be AC hum pickup!
If possible, try to borrow an exact power supply and try it. This I know is like finding a needle in a haystack! But its worth a try!
Good luck