It could be as simple as not having a working microphone connected. That is how I bought my most recent Cobra 2000 GTL. Everything appeared to work, but no audio, and people walked away not knowing that a mic needed to be connected. I knew that I could use a pocket knife to short the mic connectors to test TX/RX and audio. Bought the radio cheap, and then bought a five to four pin Cobra compatible adapter, as I had several four pin mics for Cobra 29 LTD Classic mobiles. Plug in the adapter, a known good working mic, and audio works fine.
With the Cobra 2000 GTL, it also has a selector switch for 1,2, or both speakers, while only usually shipping with one speaker.