How do I adjust the maximum fan rate or stop the fan from working overtime, it only kicks in every 20 seconds or so
"Hello, my car engine is making some weird noise, how do I increase the sound of my car's stereo speakers so that I don't hear the noise"
, lame jokes asides, your miner clearly has a problem, manually lowering the fan speed will most likely cause more problems, you should identify the problem and fix it.
Post the complete kernel logs as well as a screenshot of the miner status page, if, however, you just want to lower the fan speed, I have written this
simple guide, just follow it, you don't need to flash a different firmware, although you could if you want to.