That is the number of the program you have selected. It should be 1 to 9, not 10 as there is no program 0. You can use the PROG button to change to which ever program you want without plugging it into a computer.
If there was an error on the previous flight, you will get a siren sound and then the error code.
It talks about that on page 28 of the manual. The errors are listed on page 17 and there are only 6.
Here's a few more details on what I'm hearing.
10 low-frequency beeps, like what you hear when the altimeter is changing to a new parameter.
Pause
1 low-frequency beep (a new parameter being reported)
1 high frequency beep, then 10 high frequency beeps (the number 10)
Pause
1 low-frequency beep (a new parameter being reported)
3 high-frequency beeps (the preset that is selected)
1 low-frequency beep (a new parameter being reported)
The number 700, corresponding to the preset
Etc.
The initial 10 low beeps, and then reporting the number 10, are simply not described in the manual. Everything after reporting the preset of 3 is as normal. There is no siren associated with an error code.
Jim