Controlling fan speed on an Ati HD 4850

[tanin]

Hello,
I'm trying to lower the fan speed on my gpu. I used to do it with Ati tray tools but I recently reinstalled Windows 7 and it does not work anymore. I tried Rivatuner which doesn't work also.

I finally found Msi afterburner and fanspeed work, but both cannot lower the fan speed below 50%.

Any ideas?

Thanks

 

[refillable]

Update the driver? It maybe a driver glitch.

 

[tanin]

I'm using the latest catalyst.