Here's my guess on why the plasma is causing interference. Like CRTs, Plasmas use Phosphors to create a picture (LCD's are backlit, and use polarized light). CRT's excite the phosphorus using an electron beam that scans one pixel at a time. A plasma TV uses bursts of UV light (that you can't see) to excite individual pixels at once. They in turn produce visible light, similar to the a CRTs phosphors. All electromagnetic radiation is light, but we can only see a small slice of it. UV (that gives you a sunburn) has a higher frequency than visible light (just beyond violet in the rainbow). IR (infrared, just before red in the rainbow) is a lower frequency than visible light and can be felt as heat, but can't be seen (unless you use night vision goggles - then you can use a remote control for a flashlight). If your IR headphones really are IR (and not UV, just called IR) then UV or visible light shouldn't interfere, but the plasma may produce some IR as a byproduct of the UV/visible light. The phosphors may give off visible light AND IR when excited by the UV light. Also, anything containing heat (basically everything) gives off some IR. Since plasmas get so hot, that might do it, but I doubt it (it can't cool that fast on a dark scene). You could try looking at your fireplace the next time it is lit and see what it does to your headphones. Also, try pointing a remote at your headphones. I guess this doesn't happen with CRT's (I don't have IR headphones) so it is either because of the UV method, or they use a different kind of phosphorus (probably) that produce IR light as a byproduct. Also, if your IR headphones are analog, and if they make a digital version, that might help cut down on the interference.