[elhigh]

They claim it doesn't happen during the test drive: ride with them! Don't let them take it out by themselves.

And show them this video, of course. It points up that the issue is intermittent.

It sounds to me like the power supply for the radio itself is intermittent. That would explain why there's the spark of static as power is established, however briefly, but generally the radio is making no sound at all.

Do other audio functions work? If the CD player works, that strongly suggests that the receiver or tuner itself is failed inside the radio, but the amp and other hardware is okay. If nothing makes any sound, that would suggest the main power supply is failing.