I have a slightly strange reading of the fan behavior in the CRS326-24S + 2Q + RM.
It turns on in pulses for a few seconds (according to data taken from snmp, 5min cycle).

Is this behavior normal?
How to set the fan to run at low speed continuously?

I have a slightly different Problem with a CRS328-24P-4S+RM.
Usually the fans stay below 1000 RPM all the time. Today I connected a CSS610 to one of the SFP+ Ports using S+RJ10s and the fans went haywire.
Continuously spinning now at around 8000 RPM, people on the street can hear this thing. Looking at the temperatures, there's absolutely no need for the fans to spin so fast.
Really, what is going on with the fan control on these devices? Why isn't there an option to control them manually?

Screen shot shows SFP temperature to be at "modest" 68 °C. Without fans spinning as if pushing jet plane during takeoff SFP temperature would be nearer 90 °C. The S+RJ10s modules produce a lot of heat and that's officially a big problem.

Thank you for sharing this article, I didn't even know such wiki article existed.
Seems one S+RJ10 is enough to generate this amount of heat, the 3 other ones installed are optical transceivers.
I switched to a standard 1Gb/s ethernet port, and it's quiet again. Silence > 10G

What I don't understand is, when they already know about this Problem, why don't they release a new hardware revision, and place a fan directly behind the sfp ports?
The fans are placed in the worst possible position.

I can't say anything about design decissions by MT. But IMHO fibre connections should be used for anything faster than 1Gbps. If not for other things, UTP cables fit for speeds 2.5Gbps and higher are quite bulky compared to anything else. And power consumption per connection is considerably lower with optical SFP modules (not to mention decent range, specially when using single-mode fibres).