I'll touch on a few possibilities:
1. Do you have any hearing loss that you know of? Getting on in years and not been tested lately.
2. Are you using headphones?
3. If yes, do they have a volume control and is it turned all the way up?
4. The X50 has separate volume for speaker & headphones, you can only adjust headphone volume when the headphones are plugged in.
5. What kind of headphones? Make & model and impedance if you know it.
A. Plug in headphones, turn X50 volume up all the way, and headphone volume up all the way if applicable.
B. Set sensitivity to 15.
C. When in GB adjust mode, push the (+)repeatedly to force the GB all the way up to 20. Now slowly bobb the coil from 1 inch to 8 inches. Push (-) once per bobb, and at a particular point you should hear the audio change in two characteristics. The audio volume level should begin to go down as you approach balance, AND with a perfect balance you will hear NOTHING. Or you will come to a point where the audio level goes down and you hear both a high and low tone.
If going from 20 to 0 produces no tone or level changes, you may have very mild soil. Have you had other metal detectors in this area and been able to GB them? If yes, please post the make/models and where the knob or indicator was when GB was achieved, so the forum members can make an assessment of how mineralised your soil is.
Since this is our initial consultation I'm not going to charge you anything.
Happy Balancing
BarnacleBill