what type of fans you use, on the other side?
Turned 1 unit over so you can see it's bitmain stock fan.
Their RPM stays low with extra fan added. Very silent.
Could change both fans if you wish. But stock fans dont make too much noise when the unit stays cool.
Very easy to add front fans they can be connected directly. Just buy 4pins pwm fans.
Stupid question but your new fans are setup to exhaust (pull the air out) that the stock fans are pushing through the heat sinks?