Hello,
The speakers may be something as simple as the "fader dial" on your radio.
If the fader is not the cure, there are too many places to start.
Loose connections
Cut wires
Disconnects
Have you checked the connections in the trunk?
Sounds like there was possibly an amp installed at one time, and they took it out to sell the car. Just an idea. I don't know if the trunk release has constant power going to it or not, but if it does, that's where the Amp would be powered from, and the speakers may have not been hooked back up.
Hopefully someone can chime in w/ a cure, but I've not seen this come up before.
Later now,