Hey guys. I have a Western Digital PR4100 NAS unit. I just took out 4 of the WD Red 4TB drives out of it to upgrade to 4 of the 8TB Red drives. I am running in RAID 5. After formatting, I am getting 23.8TB of space, and the NAS dashboard is telling me all the drives passed the S.M.A.R.T. tests, and the Raid array is showing that all Volumes are active and healthy. I just moved all my media to it over the weekend. I have a little over 4TB written to it right now. Most of it is video and audio files. When I am using the unit to watch any videos, listen to any audio or look through any of the folders, everything seems normal. However, today I noticed that when idle, I can hear this odd clicking noise every 3 to 5 seconds. My last 4 drives i had in it did not do this. They where manufactured in 2014. These new 8TB drives where manufactured this past summer in June or July of 2018. When reading/writing from the disks, I can tell they are a little more louder then the original 4tb drives I had, but I also heard that was normal because they where a larger capacity drive. However, this clicking when I am idle had me some what concerned. Is this normal? Or a concern? I've read a few different posts related to this issue. I am seeing terms like 'Head parking' or that it could be doing 'background media scans'. Any thoughts? Thanks in advance for any replies.