My guess is that the CPU was busy when it beeped, thus sometimes the interval is short and sometimes its long.
The beep pseudo code is usually as follow (example of double beep)
- play beep audio (1st beep)
- thread wait or while loop
- play beep audio (2nd beep)
So during the "thread wait or while loop", if the CPU happens to be busy (or waiting for some component to finish its work), then it will cause it to be longer, thus slower beeps.
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