Unless one of the sys fans is momentarily stopping/re-starting so fast you can't detect it with the eye, the problem may be the board or BIOS faulting. Unplugg the sys fans one at a time and see which one is triggering the msg. Then swap them with the SYS fan headers and see if the same fan or the same header is causing the error msg.
Of course, you could always connect the fans directly to the PSU's Molex connectors if the board is the issue.
I pulled out each fan like you said and it turned out that I had a faulty fan. I got a new 120mm and that solved my problem. Thanks!