I've had my current GV for over 2 years now and during that time, the radio/DVD/Sat Nav occasionally loses it's sound. When this happens, the radio always starts with sound when I first start the engine but the sound goes off after a few seconds.
The radio displays everything, it's just the sounds that goes off. Usually the sound will come back on after 2 or 3 days without my intervention.
When I first bought this GV there wasn't any sound at all but I read that a firmware update was available on the latest Sat Nav discs so I bought a set, installed the firmware, and the sound came on.
The radio can play perfectly for months but then can lose it's sound for no obvious reason.
Today I pulled the neg battery connection for 15 minutes in the hope that it may bring the sound back, but it didn't. But on my way home I stopped at a shop, turned the engine off, came out of the shop, started the engine and the radio started playing!!!