Hi Andy,
I use substitution to solve these 'mystery' faults :-
ESC with different motor
Different ESC with planned motor
By-pass 'jumper' leads instead of the usual connectors (be careful not to 'short' anything !)
etc. etc.
Motor 'beeping' is usually a sign that the ESC is confirming a programming command. Different beep patterns confirm specific commands eg Soft Start, Motor Braking etc.
Best consult your ESC /Card instructions to see if a regularly occurring beep is, in fact, a valid command.
Failing this, consult the manufacturer's website "FAQ" section….it's likely that others have also seen this condition too.
Good hunting,
Dave