Hi, i have three RB1100AHx2 on the bench (two of them run the FANs at 100% all the time), and a third one (very quiet running), for "differential-diagnose".

the FAN speed seems to be derivative of measured current via 3x-parallel 0.22Ohm resistors, amplified by a Tl072, and fed into Q1106, and with a pulldown to ground to some other circuit.

It appears that 0,5volts from Q1106 mean silence, and 0volts mean full-noise.

Does anyone has experience with this subcircuit part, and could help me finding what is Q1106 and it's associated resistor?
It also could have todo with Q1105/1106/1107, for which i found no reference.

Get an Y fan splitter and connect both fans to main if you want lower noise.
That is what I did on all AHx2 units.