When I first built my Arducopter I had no idea what the various sounds it made meant. Now I have some familiarity with it I thought it may be worth sharing.
First thing to know is the sounds come from a couple of places.
For me the first sound is from a jDrones battery monitor I have fitted to my Arducopter. It sounds like this: Battery Monitor.wav If I run my LiPo battery voltage down below 9.9 volts this tone sounds continuously to warn me to land 'right now'.
Then the second set of sounds is from the electronic speed controllers (ESC). Note the ESC has no beeper of its own, instead they command the motors in such a way that the motors emit beeping sounds. So do not expect beeps unless you have your motors connected.
A normal ESC start up sounds like this: Arducopter ESC normal startup.wav
If the ESC control cables are not connected or the APM is not correctly configured then after start up the ESC will continuously emit beeps every two seconds. It sounds like this: Arducopter ESC no throttle signal.wav
My Arducopter also beeps when in CLI mode I connect to it with USB: Arducopter CLI USB Connect.wav
I hope this helps any new builders to understand their Arducopter and is various beeps. If anyone else has any Arducopter sounds it would be good to share them - just not spectacular end of flight sounds - we don't want to scare off new players