I found the best thing since sliced bread...http://www.amazon.com/Scosche-Audio-.../dp/B0007THIDQ
It's not wireless so there's no interference. Not to be confused with an FM transmitter. Basically it adds an AUX input to ANY radio. No searching for a clean channel.
It feeds your audio signal from a headphone jack ( or RCA cables) by FM modulation, directly into the antenna input on your radio bypassing the antenna when on, allowing the radio to work as normal when off. It comes with an On/Off switch.
This is the answer. Totally versatile.
Here's one in action -