Pull the radio fuse. Any power supply capacitors should drain within a few hours, but I recommend waiting overnight, the restore the fuse.
If power-cycling the radio in this way clears the issue, it may have just been a fluke or the issue may soon return. I do believe the speaker you reference is powered by the head-end, so replacing that may be the only permanent solution. Please seek more members' points of view. My wife & I have had very little trouble in the six-plus years we've had our 2 cars.
The reason power-cycling systems on the STS requires physically removing power is that virtually all switches are virtual and merely send instructions to devices in standby to power up or shut down. Fuses are usually easier than completely disconnecting system or subsystem.
If all else fails, disconnecting the car battery also cures a lot of temporary ills, too. The wait for module power supply caps to discharge can be eliminated by touching the disconnected cable together.