When connecting the earth to an audio/video set, it nearly always comes to an annoying humming from your speakers. This is caused by a so-called ground loop. This loop consists of the earth of your system, and the earth of the cable antenna for TV and radio.
The earth of your system will be the earth of your home electricity system, which may be physically far away from the earth of the cable antenna. This will inevitably introduce an voltage difference between the earth of your home system, and the earth from the cable antenna. By connecting those two different earth systems together in your set, an alternating current will start to flow that causes a 50 Hz hum in your audio.