Not a chance. Grills are purely cosmetic. A really badly designed grill will degrade the sound when it is on (due to blocking some of the sound coming out of the speaker). But a properly made grill is purely cosmetic and just there to cover up the "ugly" drivers.
Old CRT "tube" TVs used magnets to "steer" the electron beam that comes from the cathode ray tube and creates the image on the screen by activating phosphors on the screen and causing them to glow. Since speakers have strong magnets in them, it used to be possible to screw up your TV's image by having speakers too close to the TV. So most speakers have "shielding" in them, which is just another magnet that counter-acts the "stray" magnetic field of the speaker's driver magnets.
But LCD and plasma displays don't use magnets like the old CRT displays did. So they are immune to any interference from the magnets in your speakers. That's why, these days, lots of speakers are foregoing "shielding", since it lowers the price and also allows for more efficient speakers.
Bottom line, with an LCD or plasma TV, you don't have to worry! Especially not about the grills on your speakers
