Ringing in Ear at Low/Any Volume with new Car Stereo?

I recently changed my Toyota stock stereo for a Panasonic stereo & Sirius receiver. I now get ringing in my left ear at any volume any time I listen to the stereo whether FM, Sirius or CD. It now sounds worse than my stock system. Could something be wrong with the wiring causing some inaudible feedback? I went back to the store (Fry's) and they tried to get me to buy better speakers. Has anyone experienced something similar? I want to emphasize that this occurs regardless of how softly I play the stereo.