Recently m also face same issue of continues beep. In this situation array showing degraded.server working fine and server stop in post to press any key to continue.that time continues beeps are started. actual issue is with one HDD failure in server. It is the beep of HDD failure.so simply replaced the faulty HDD with new one and after rebuilding post error removed and server beep is also stopped.
If you found the issue with HDD and u want to stop this beep u can stop it by dell server administrator, in storage option- a pull down option and select Disable Alarm. It will stop the alarm in server, but storage showing degraded u have to replace that faulty HDD with known good one.
I have read all the manual trouble shooting guide of Dell but dell not mention this issue in there document.