Yeah...those could be your LDW (Lane Departure Warning speakers). They are supplemental to your radio speakers. Usually 3rd party collision mitigation systems are designed with their designated speakers.
You should have one on the corresponding passenger side as well.
Wow, thanks! The LDW system seems to be inactive, I wonder if the speakers got "unplugged" when this was a company truck. Would be cool to wire each of them up to different CBs, one on 19 and the other on scan.