2x HR-09 M.2 heatsinks.
New NAS has m.2 (sata not nvme) cache drives. I'll get a small bursts of 300MB/s transfers then suddenly drop off. After some investigation turns out these cache drives are thermal throttling. The owners manual actually suggests only using m.2 drives with heatsinks on them. Previous owner didn't take that into account, might have been one of the reasons they were unhappy with it.
They are going to be rotated the wrong way to really take advantage of the natural air flow of the NAS. So a little 40mm noctua fan I have laying around I think will help with that or maybe I'll 3d print a duct to help out not sure about that part yet. Get the heatsinks installed and see what happens.
(would be nice to swap out the 70mm fans as well but thats an odd size to find a quality replacement that isn't as loud)