Transfer the hard drive from a failing Readynas 312? Planning for inevitable failure..

The only thing in the NAS that makes any noise is the fan.  So it may be one of your drives, not the NAS making the noise, indicating it may be on the way to failure.  But since you have a spare, the easiest way to find out is to do the transfer.  None of the configuration is saved in the NAS itself.  So just transfer the drives over with power down and the new NAS will come up and look just like the old one.  Just be aware that if you reserved an IP address in your router, that's based on the hardware MAC address, so will change.  If you have a static IP, then it should stay the same.