NAS Model: PR4100
Hard Drive Model: WD4002FYYZ-01B7CB0
I recently installed a pair of WD Gold hard drives, which were fully tested prior to installation. The installation (non-spanned JBOD) and data migration were successful, and no serious problems were encountered. However, I began to notice that the drives sounded like they were being accessed when they were idle, so I began a process of elimination to try and isolate the cause.
The sound itself is best described as a sequential repeating pattern of low tics (not clicks) followed by a brief grunt, and an occasional burst of activity sounds. It sounds very much like the sounds a hard drive makes when it is being tested or wiped, as if groups of sectors are being sequentially accessed.
I first thought the sounds may have been a NAS file indexing service, but one of the drives is currently empty. I also eliminated the possibility of network activity by removing both network cables. I even removed each drive and connected them, one at a time, to my desktop computer to see if they made the same sounds, but both drives were very quiet when idle. Just to be sure, I used the WD diagnostics program to perform a short test on each drive, but all active sounds were comparable to normal hard drive sounds.
Both hard drives are working perfectly, having passed all tests, and their S.M.A.R.T. results (RAW_VALUE) are exactly what they should be for brand new drives. In addition, the LOAD_CYCLE_COUNT is not increasing dramatically as one might expect to see if the sounds were caused by head parking activity.
By process of elimination, I can only conclude that the hard drive idle sounds are somehow caused by the NAS, but I do not know how or why. Both drives sleep normally, and the sounds stop until one or both drives wake. None of my WD Black hard drives (WD2003FZEX-00Z4SA0) make similar idle sounds when installed in the NAS. In fact, two of them are installed now.
Have I missed anything? What could be the source of the sounds?
BTW: Please don't direct me to links about normal hard drive sounds or tell me to contact WD support. I know what hard drives sound like, and WD support is generally very unhelpful.