Electrical System Brainteaser

When 'Shurflo' first came out with a roof vent exhaust fan I purchased one and installed it in one of my roof vents. Then I started burning out light bulbs, the little bathroom exhaust fan, even the batteries were getting overheated, etc. I checked the voltage on my light fixtures since they seemed to get brighter every time the 'Shurflo' fan came on. Sure enough I was getting readings of more than 20 volts! The fan was feeding higher voltage back into the 12V system when it was operating! I contacted 'Shurflo' and they admitted that their ceiling vent fans were causing some problems in some trailers. They had redesigned their circuit boards as a result of these problems and added a diode to boards where the power supply was connected. They sent me a diode to connect between the incoming power wire and the connection to the fan and all my problems immediately disappeared.
I would suggest that you go to an electronics store and pick up and install a diode to the wire that connects your radio. I think that will solve your problem.