mine was doing the same and it was the curcuit boards, one of them was bad and was melting the plastic over the wire on my left brake bulb. I fought it for a few months cause i checked the wires in the bulbs and they werent blown, then i finally took it out and sw the plastic had been melted over the connector

 

I had the same problem on my 03' on the right rear. It turned out to be the plastic flang that holds the bulb itself. It didn't hold the bulb in tight and caused it to jiggle around giving that indicator light. Take and look at the connectors leads on the back of your bulbs and if it looks burnt that may be the problem.