Like many other threads on here, I found my new DS-7608NI-K2-8P unbearably loud. It has a channel well technologies PSU (KSA-180S2) with a 12v 5A rail, a 52v 2.5A rail and a really noisy 40mm fan, and then a second not-quite-as-noisy 40mm fan on the case.
Everyone has a different sensitivity to this sort of a noise so I've seen some people say it's fine, and that's great for them. But mine was shut in a thick walled cupboard with a heavy tight-fitting door, and it would still be loud enough to irritate me enough if sat in the same room, to have to change room. These sort of fan noises have a quality factor as well as a loudness factor, and the NVR PSU was definitely on the nasty noise side a metallic, slightly varying and grating on the mind noise.
Anyhow, I've seen a variety of people on forums replace the fans to slight to good improvements, but if I was going to cut into the box around I wanted a full solution to make it (virtually) silent. I've also seen a number of people suggest replacing the power supply with external bricks, though not actually do the work. So that's what I've done.
This is a 60W 12v 5A power brick from Channel Well Tech I used for the first rail. The three yellow wires on the existing CWT PSU pigtail are all positive 12v, the black wires ground
https://amzn.to/2RxxRzf
This is the 52V 2.7A power brick from DSLRKIT specifically for PoE which is why the second rail needs the greater power, which I used for the second rail. Unfortunately Amazon has stopped carrying it since I purchased it. No idea if that is a good or a bad sign, but you'll find the same model elsewhere, or I'm sure other PoE power supplies would work. The old pigtail is 52v positive red, and black ground (at least consistent - but do check on yours!)
DSLRKIT AC 100-240V to DC 52V 2.7A 140Watt Power Supply: Amazon.co.uk: Electronics
These both come without kettle leads, you'll need two (I had some old ones kicking around)
https://amzn.to/2S3BmlU
I used a Nexus 92mm fan. Nexus make (made?) superb fans and I use in my silent PCs this one I had spare. Unfortunately their website is either down or they aren't trading any more. Basically just get a high quality fan of as large a diameter as you think will fit in the case. Silent PC review will give almost all the info on fans. One of the things they are good at is dealing with the subjectivity of fan noise, not only will these fans be REALLY quiet, they also give off a very neutral/softer (to my ear) much less obtrusive steady white noise. Basically though any high quality 80/92/120/bigger fan from Scythe or whomever, is going to be enormously better than the original 40mms and move plenty of air.
Fan Roundup #6: Scythe, Noiseblocker, Antec, Nexus, Thermalright | silentpcreview.com
So putting it together then.
The most likely thing to get wrong here is connecting the new power bricks to the pigtail in the wrong way and frying the board. So use a voltmeter and measure twice, cut once.
In general if you aren't comfortable with working with electricity, a voltmeter and a soldering iron stop. Or if think your boss will object to what you're doing with the kit, or the PAT tester might next time they visit the office also stop!
Steps
Carefully checked all the positive and negative voltages on the existing setup and the new bricks and labelled positive really carefully.
Removed the old power supply
Cut the pigtail off the old power supply, chopped the plugs off the end of the power bricks, and used chocolate block connectors to connect a to b
I wired the fan into the same 12v power rail and hot glued it to the bottom of the case where the holes are.
And then reassembled and plugged it in. Works fine (pictures enclosed)
Sound level.
Now acceptably quiet, quieter than most of the laptops in the house, I'd have to concentrate to hear it over this laptop with the cupboard door shut, with the cupboard door closed it's basically unnoticeable. The noise in the cupboard if you put your head is now a much more tolerable shhhhhhhhh noise, rather than the shrieky and grindy old one. But the 92mm fan at 12v still makes an appreciable amount of noise, and there is a lot of nasty aluminium undamped, un-braced surfaces in the box, so it definitely could be a lot quiter.
So there would be a lot of things that could be done to improve this from my PC silencing experience, and I would have liked to have done with more time and energy, but I was in a hurry to shut the thing up. But if you're doing something similar, you might want to consider...
Things which you might want to do which I didn't ....
Connectors and back plate
Adding nice connectors to be able to plug and unplug the two power supplies, and closing off the old hole where the power connector is. Mine is basically wired into a cupboard so I'm not too fussed. But you can have some grasping cable entry grommits and there are screw holes around the hole to fit a plate. That would definitely be a good thing to do.
On connectors.
Originally I'd planned to get sockets for the PSU plugs so you could plug and unplug the two power supply units in, rather than having the bricks permanently attached. I didn't because the two power supplies have a similar enough plug you could very easily plug the 52V into the 12v and fry everything. It would however of been much nicer, so if I were going to do this, I'd look to replace the 52V plug with an oversize plug and socket to make it impossible to plug into the wrong one.
Hole
Cutting a hole for the fan (especially if you had a second hard drive so couldn't use the existing vents) might be good. There is lots of room when the power supply comes out to do this in either the lid or the base. There are enough holes in the base for this to work fine without if you don't need the second drive, but a nicer hole, a fan gasket and some fan mesh would be better. Cutting neat holes in aluminium isn't straight forward at home, so a fit from the outside fan mesh which covers your work is a nice thing.
Rubber Feet
The NVR has small stand-up metal feet to get the base somewhat off the surface below. So the fan does actually work fine like this, but some nice rubber feet for the NVR will improve airflow a lot and reduce noise further. I couldn't find any feet in the bit box, but will probably locate some. If you were fitting new fan meshes you'd definitely want the additional clearance.
Fan gasket
I hot glue gunned the fan down, which provides for an air tight fit over the holes, but means it's tightly coupled to the case, and the case is nasty flappy unbraced aluminium which normally contributes to a bad noise. If you can afford a nice silicon fan gasket it'll reduce the noise substantially again. They always seem very pricey to me for what they are.
Fan speed reducer.
I couldn't find my old Zalman Fanmate-2, but if I could I've had used it, just connecting it in line to the flan. A 92 mm fan at 12v moves a lot of air, way more than needed having taken the power supply out of the box. This would let you reduce the fan to 7v or 5v (or where-ever you wanted really) Big fans at 5v really are very very very quiet and still move a decent amount of air.
Case damping or noise adsorption material
I used a little (just what I had lying about spare) on the case above the hard drive. This stuff is always over-hyped, it's not going to make a big difference on it's own. But I do find it helps in improving the overall quality of the noise, even if the total volume is about the same. If you were going for a thorough solution I'd cover the whole of the case roof and any exposed large surfaces of the floor.
Harddrive mounting.
The harddrive is now a noticeable part of the noise from the box. The bottom in screw mounting is very difficult to damp and still make transportable. Some side mount damped connections fixed securely to the base, and then with damping material running underneath would be better and still fit under the lid.