I was just about to say "throttle calibrate" but you have fixed it. Good oh!
Alan, I have found that the cheap ESCs are more prone to this. On some of my foamies I get similar beeps now and again. I have found that some ESC are slow to find throttle, so leave alone for a bit longer. (Restrained model) Or I disconnect battery, put throttle to high, reconnect battery and as soon as the first beep is heard quickly slide throttle to to low. (I assume your thr sub trims are neutral)
Programming sequence is generally generic, ie; first beep is "brake on/off, etc.
Edit: Throttle range not being recognised. Put all throttle settings to neutral and rebind RX.