I don't think you can set the actual beep sound for when someone 2-ways you. Under profiles you set the DC/GC to Tone, Vibrate + Tone, Vibrate, or none. There is no option to select the actual tone.
For a DC ALERT, you can set the sound you want it to make, but this is different then the normal 'chirp' you hear when you're actually talking to someone back and forth.
If your 'chirp' isn't working, I'd recommend removing both your battery and SIM for 30 seconds and then trying it again.
No longer a BES Admin, but it was fun while it lasted!