So I noticed that many people who bought CRS317 as "home" switch replaced fans with Noctua in order to reduce noise level. I decided to do that as well so I guess I'll make small write-up about this topic.

Lets start from basics. If we want to replace something, first we should know what are we actually replacing.
I have no idea if it's good or bad but it's 12V so I got 12V version of A4x20 PWM Unfortunately it's not as straightforward as slapping new fans and calling it a day. Screw holes in CRS317 are too small for rubber mounts so I had to mount them from the other side than standard. Due to small size of fans and really long rubber mounts I had to cut them:
Unfortunately it's just beginning of issues. It turns out fans don't start up between 40 and 50 degrees on CPU and slightly "kick" trying to spin up. Without success:
https://youtu.be/5N7HqJdii7c

I set up small lab to figure out whether they will eventually spin up (laptop blowing hot air on CRS317 heatsink):
And yeah they do, after reaching 50 degrees on CPU. Which is not that bad but it's something to keep in mind. I found this thread bringing up similar topic:
viewtopic.php?t=132506

While it's no longer true (fans do spin up properly during initial startup), it's still somewhat relevant. Also yeah, it'd be nice if those options in CLI actually worked because as of now - they still don't do anything. Problems don't end here though. NF A4x20 seems to push significantly less air than stock fans and provides waaaaaaay less static pressure. It made me a bit worried about cooling of unit, especially considering far from perfect placement in desk so I soldered and assembled custom small fans controller hooked up to adjustable 3-12V power supply:
So final setup looks more or less like this:
Comparison of temperatures before and after goes like this:
Before:
After:
So... how's aftermath? Well, switch has higher temperatures because there's inferior airflow, due to additional 120mm fans is not all that much quieter, warranty is voided, money spent on fans. That was nice day

All in all - if you have CRS317 as home switch for lab or something then maybe? It's somewhat worth it? But for any even remotely production-like use big nope.

hi,
i did the same change - went with Noctua NF-A4x20 PWM. Two pieces. I still thought they were little bit too loud. Played with Noice Reduction extensions that lower speeds by 20%. Still noticable at max speed down from 5000RPM to 4400RPM. Then tried to put 2 fans on 1 header and connect 2 noice cancelling in series ... max speed was 3400 ... that is fairly quiet.

But key thing is - with optical transcievers (SFP+) ... and latest firmware on CRS317 CPU temp hovers about 40-42C in 22 degrees room and fans don't switch on .... only when i used 2 SFP+ to RJ45 adapters (next to each other) - those temps are up to 70C right now and above 70 fans do switch on for a minute or two and then it drops to about 2000 RPM for another minute and then fans switch off ... with some distance between ports they do not switch on at all.

So my experience - if no SR+RJ10 adapters (RJ45) being used or just one or two your CRS will likely be silent ALL the time.
If you have few of 'hot' adapters - above 70c fans will switch on.
Using Noctua fans will make it very bareable.

I also have CRS-305 and on it SR+RJ10 reaches 80C+ temperature but since it's fanless device i THINK Mikrotik could allow instead of 70c maybe 80c to be clip level for turning fans on.