Weird fan problem please help!

So I got Black Ops 2 for christmas but my computer is broken. So I put my 4870hd 1gb in my Dell XPS 400 so I could play it there until I got my rig up and running. Haven't played yet because I can't take listening to the flippin fan! The speed just increases and decreases from what sounds like 30% to 80% every ten 5-10 seconds. It is so loud and annoying I can't take it. Whenever I try to change the fan speed it doesn't do what I tell it to. I keep trying to change it with Riva tuner, AMD Overdrive, and speedfan but nothing happens. I'm using a 650w PSU and everything seems to be working fine besides that stupid fan. And it IS NOT overheating, its staying at like 35 degrees. PLEASE HELP!

So what OS are you running, which fan are you referring, what CPU and any mods?

oh well i moved my gpu back to my old pc that im fixing... But I will tell you anyway. Its a dell xps400 all stock parts besides a 650w psu and an ati 4870 with 1gb so its the base model with the red ati fan on it. Windows 7 32bit, dont know if its ultimate or what... pentium D, 2gb ddr2 memory (512x4) anything else you need to know?

oh and i was talking about the gpu fan, the red one on the ati 4870. not HIS, not saphire or anything JUST ati.

If you want something quieter jump on somewhere like newegg and search for vga cooler, you will find plenty of options to fit your card.