I think what your cousin may have heard about, is that some guinea pigs may suffer stress from being housed right next to a noisy television. They're skittish animals by nature and some may find both constant and sudden loud noises stressful.
I have three guinea pigs. Two of them couldn't care less about what noise anything makes - they're completely unflappable. The other definitely would be a bit jumpy if I put their cage next to the tv - she's just not as relaxed about external noises (and movements).
Even when they seemingly get used to things, they can cause guinea pigs stress. So if your guinea pigs do react to sounds on the tv, it's best not to put their cage near the tv (at the other end of the room is fine). I can't imagine it killing even a very highly strung guinea pig, but if it does tend to bother them, it makes sense to keep them a good distance from it.