Before we throw money at this... (SAT/NAV Radio issue)

[RenaissanceMan]

So my brother just bought a used 3.0i E53 almost identical to mine, except he has the SAT/NAV option... Car had a thorough PPI but they missed an issue related to the radio. When you first start the car, the radio works, but after about 20 seconds the right side speakers shut off. This happens every time. Fooling with the balance and fader controls don't do anything to help. Is this a problem with the radio module under the spare tire? Programming issue? Head unit issue? Any help would be greatly appreciated!