They could of kept the miners in a filtered room without dust OR they could of just replaced the heatsinks and fans.
The Chinese aren't wasting money on filtered rooms. That's why they're winning

also would adding a back fan decrease the temps enough to slow down the front one??
what if i used one of those fan speed adapters.. im assuming the fan is just a regular 4 pin pwm connector?
i have a few of those that come with CM fans that are preset to 1800 and 1600 and 1200. altho i think those speeds are set for a 2500 rpm fan, i think its 70% 60% and 50%
No, not enough to make any significant difference. You
could use a resistor cable but I can't think of one which is rated for the 1A+ the fan uses. That's 2W of reduction that tiny resistor has to dissipate, a huge huge amount. Replace the fan if you want to get it quieter.