If a single hard drive fails and is making any odd noises, it’s important to power the drive off, and leave it off until you can get it to a data recovery professional. Further attempts to read the drive or copy off data will almost certainly cause further damage to the drive, and may well render it completely unrecoverable. This can occur if there is a failure of the read/write heads; allowing the drive to continue spinning could result in the damaged heads scratching the platters, leaving absolutely no chance of recovery.
With RAID, there are more options. Many causes of failure are the result of a crashed RAID rebuild (following swapping out a failed drive with a healthy one). At this point, you need professional assistance. A power surge can leave more than one drive damaged – enough to bring down the RAID. This needs immediate professional attention.