Hi unholythree,
I'm in a similar boat. I just got the same SGI unit, and the fans are very loud.
So far I swapped the two 80mm for two quiet units.
However, like you, I have found the culprit to be the PSU's 40MM fan.
I ordered a Noctua 40 A4X20 40mm fan, and have it standing by. However, I...