Radio Volume is 0 or Max

Hi All,

I just bought a 2008 Prius and the seller has lived with an audio issue for the last couple years. When I go to play the radio there is no sound, but when I turn the volume knob to level 1 the speakers max out. I went to settings and set the audio to only play through the rear passenger speaker. The same issue occurs and when I turn the volume up further the other speakers go in and out as I twist the volume knob and always at max volume. It's the original radio. Any suggestions?

Thanks!