Server making continual beeping noise......

Sounds like one of two errors - either one of the power supplies has died (not sure if the 1800 has redundant power supplies or not) or a drive in the RAID array has failed. Most likely it's the drive. Run the Dell Server Administrator tool to check the health status of the array, sounds like you need to replace a drive. Most RAID systems fail if you lose more than one drive, so I'd replace that drive ASAP.

The beep tone(should be continous) you are refering to is that of a failed drive Usually the perc card will emmit a continous beep if there is a hardware failure.If you can,enter the Perc Utlity there it will show you which drive has failed.You can also silence the alarm there aswell.Replace the failed drive.If it does not automatically rebuild set it as a hot spare it will start to rebuild then.
Good Luck