Depends on the fan. I've seen plenty of fans that people put into machines and are connected straight to the 4-pin molex connector which without some type of controller it runs full bore all the time. If the bios can't control it then you may need to see if it's wired to the motherboard via a 3 or 4 pin fan connector and check if the motherboard is able to control the header that it's plugged in to.
There should be some method of slowing it down through the BIOS then. Look close at the connector and see which header it it. It will be something like CPU1 or SYS2 or the like. Then it should be as simple as finding it in the bios.