Chenbro
From Indie IT Wiki
Stop Warning Beep Case Alarm
The warning beep is just a signal to say one of the fans is not spinning. It may just be dusty.
To stop the beep:-
Find the fan on far right when looking from front, remove. Below it you will see a speaker with a line of jumpers, remove the jumpers at both ends - that will stop the beeping and may well spin the fan back up.