not a good idea. I have eight units
 2x m10
2x m30
4x m50

all of them have hot exterior that is deliberately done.
all of them are long with larger fans
only two fans that do about 310cfm each
with the long length heat sheds to outside walls of the miner.

If you want to reduce fan speed try two long heat sinks on the left and right outside of the miner.

thus the ability to shed heat on those walls would lower internal heat.