Quoted:
Any ideas on the noise and how to fix that?
Wes
I do have an idea...
It may sound whacky... but, I have seen it before.
You have three fans, each has 3 blades on it. The electricity that runs the fans has a 60Hz switching frequency (the voltage changes polarity 60 times a second).
I have seen 3 and 6 bladed fans do this wierd synchronizing deal where they all spin at the exact same speed, and the fan blades align with each other.
This can cause a wierd 'pressure pulse' which creates a 'standing wave' in the room. Basically, the blades sync with each other and create sympathetic pressure waves that build on each other, causing strange acoustical patterns in the room.
Does it sound the same everywhere in the room, or are there locations where it is more pronounced (pressurized) and less pronounced (rarefied)?
Try running the fans on different speed settings (one on med, one on high, one on max) and see if it happens then. Also try 2 on max, and 1 on high... see if it changes at all.