So, this might have been going on for a while since I've been thinking the stereo hasn't been sounding too good lately, but the other day clinched it.
I was listening to the radio and had occasion to turn it down quite low and then I realized there was almost nothing coming out of the left channel. I played around with the balance and confirmed the left was just a whisper and the right quite strong.
Just as a crazy notion I tried putting a CD in and voila! Sound in both channels! I took the CD back out and now the radio was working fine, too. It worked like that until the next day and then same thing. This time all I had to do was change radio stations and the left channel kicked back in.
Since then I've noticed it's most likely to stay fixed until I shut the car off for the day and then might cut out again at next start up.

Any ideas as to what's wrong?