back to the analyze of reason(s). You need use pencil and paper to write scenario evaluation
1. Vibration and noise relation inspection.
A. Touch the metal plate (all sides) of the
RS819 by fingers and try to find a vibration location.
B. Same for the all disk bay (front)
If no success, continue step by step:
- disconnect all external cables (Ethernet, USB, eSATA if any) except power cable. Test again entire point 1. procedure
- if no success, pull out disk no. 4 (from right side). When no change, even with again entire point 1. procedure. Continue with disk 3, disk 2, disk 1
- there is also possible vibration between pair of the disks. You need to check it.
When you find a disk bay as vibration reason and the disk is from S.M.A.R.T metrics OK - you need find a way (in this forum ) how to kill it
If there is a disk problem, change the disk.
When there is still not a success and your NAS is not under warranty (but its early 2019 model):
- switch off the NAS
- disconnect all cables (power, Ethernet) from the NAS
- open cover of the NAS.
- you can find 3 small 40x40mm fans on the rear side, check it, also clean a dust from them
- same for PSU
If there is a warranty - you need contact a seller. Don't open the NAS!