The Bose subwoofer is terribly detrimental to the sound quality in the Volt. They inexplicably seemed to have tuned the port to the resonant frequency of the car. Anyway, if you want accurate sound you can disable the subwoofer in about 10 mins with 1 socket wrench required.
Lift up the hinged floor in the back of the car (the subwoofer is under there). There are 4 nuts holding the plastic tray down to the floor of the car. Remove those nuts (10mm I think it was), pull up on the hinged floor and you can get the plastic tray out.
Under the tray you'll find the 12v battery, the subwoofer enclosure with amp mounted to it, and a blower motor for cooling an electronics box that lives back there too. On the left side of the subwoofer enclosure, there is a 2 pin speaker connection - simply disconnect it and the subwoofer will be disabled.
Obviously do this at your own risk, I don't believe disconnecting the sub causes any problems, but I'm not providing a warranty on your work. I don't think there are any high voltage connections back there, but like I said, do it at your own risk.
On the up side, the frequency response can finally be (almost) tamed. Check the pics on flickr