Based on everything I've read, the PWM signal comes from the ECU (pin 8) through a small purple wire to the fan module. I will backprobe the ECU with an o-scope to check if there is a square waveform. I discovered that my OBD2 scanner has a bi-directional control to activate the fan, so that makes testing a lot easier.

Best guess (before testing) is that the ECU is putting out a good PWM signal and I will need to trace the control wire to figure out why the signal isn't reaching the connector to the fan module. I've watched a couple Youtube videos where they found this thin signal wire was frayed/broken.

 

That is really weird and goes against basic electrical design practice. I need to check the service manual....

As I suspected... the ECM doesn't send the full PWM signal to the fans.

"The fans are operated by the fan control module that receives a 0 to 100% Pulse Width Modulation (PWM) frequency signal from the ECM. The ECM varies the PWM signal based on inputs from various sensors. The fan control module uses the PWM signal to determine the required output voltage to the cooling fan motor(s)."

It would have made no sense to have the ECM produce the full load to run the fans, so the ECM sends a PWM signal at low voltage to the EFCM (Electronic Fan Control Module) based on a number of sensors, and the EFCM then determines what to send to the fan motor. A single fan motor pulls as much as 500 watts, dual motors 750 watts! You're right in that pin 8 out of the ECM is the PWM output signal, but you also need to check what's coming out of the fan module to the fan.

 

OK, I purchased a 12" long bit from HF and got to work. To keep the hamster cage from turning, I placed a screwdriver into the cage vents which kept it in a fixed position. Then the hole drilled nicely.

I inserted a plastic drinking straw into the hole (photo attached) as an extension for the straw on my White Lithium Grease spray can. Worked like a charm.

Result: The noise is reduced by about half. Glad for this improvement, but I was hoping for a little more.

 

I spray mine annually but it's still annoying in the spring and fall. It's low frequency but my hearing is quite good and I can fixate on it !