That’s correct (although not our Basic ESC 500, if that’s relevant) 
There is indeed a parameter for it which can be configured:
The startup beep volume is currently set a bit over half strength.
There is also a beacon volume option, for beeps the ESC can emit when it’s armed and sees zero throttle for an extended period (e.g. to help find a lost vehicle), but that volume setting is irrelevant unless you reduce the beacon delay period down to a finite value (we’ve configured it to be infinite by default, so beacon beeps never occur).