There's 3 fan connectors?
One at the top of the board between the RAM slots and the CPU heatsink mounting bracket, one at the bottom of the board underneath the 3 PCI slot and one right next to the floppy disk connector?
I've tried to find the best pictures of this board so i'm gonna need some help here.
But like you said it didn't have a system fan before.
Check that the board is mounted square on the mounts and thats it's clean.
Also go into the Hardware Monitor section in the Power tab of the BIOS and see if you can disable any fan speed warning/temperature threshold settings.