RepairPal Certified shops can diagnose and repair your 2006 BMW 525i. They provide transparent pricing with a minimum 12-month or 12,000-mile warranty on repairs and services.
This happened in my 2009 128i and it was short in the system that caused both the radio and the amplifier and wiring to need replacement. $2500. BMW paid since my car had only 11000 mi. on it. Good luck.