Recently I noticed that the left channel on my car radio only worked intermittently. I just assumed it was a problem inside the radio and was planning a visit to the dealer since it's still under warranty. But then it occured to me that it might be a loose connection since I added an adapter 2 years ago when I added my XM radio. Sure enough, when I took the radio out, one of the connectors was loose. I pushed it back in until it locked in place, and now I get sound from the left channel. The moral of this story is to trust your gut and check your connections!