My fan has been running for days. I just check my health status and the drives are 46° C and the fan is running at 9090 rpm. I do not see anything blocking the vents.
I suggest to test the drive, you can have a look at this KBA:
I had a defective unit at first. System Test menu showed faulty fan, returned and got a new one.
I’d check that first.
The fan is small and when spinning up it makes noise, wish it would be a much larger, lower rpm fan…
Then after copying pictures (mainly raw) but also jpg) onto the NAS I had the fan spin forever…
Since then I deleted all raw from the NAS and only keep downsampled jpg’s on the NAS.
I back up all native picture files on external HDD.
NAS tries to create thumbnails from everything and you can’t turn that off, a real nuisance.