I can speak only for Q500. I do not know what excacly you hear but usually after ESC or motor exchange a motor assignement is neccessary. Connect it to GUI, check all sensors and do motor assignement.
Another source of unmanted beeping is an uncalibrated remote controller, right stick. If it is not excactly on zero in middle position the drone will report this with constantly beeping. Check stick values in HW-monitor at ST10+.
Hope for H920 someone else knows the beep codes. Beep code may give an hint to motor 2.
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