These beeps are indicating the input signal and arming state. The low beep means a pwm signal is detected, the high beep means that a zero-input signal (1500us) is detected and the esc is ‘armed’. So I think @williangalvani is on the right track of looking at your neutral signal. If you don’t have an oscilloscope or logic analyzer, you can try shifting the number 1500 in your code around. Try 1510, 1490, 1480…
Your pwm frequency (60Hz) is a little bit low also. Try 200 or 400 Hz.
Here is the firmware manual: https://bluerobotics.com/wp-content/uploads/2018/10/BLHeli_S-manual-SiLabs-Rev16.x.pdf
Note that Blue Robotics ESCs are programmed differently than most escs where the zero-throttle signal is 1500us rather than the usual 1100us. Did you purchase the ESCs from our store?