HD4850 Fan Speed Fix
http://forums.vr-zone.com/showthread.php?t=295165 if you make a profile in catalyst after turning on Overdrive( make sure clock and memory settings are correct).
You can then go to the file "C:\Users\Bretware\AppData\Local\ATI\ACE\Bretw are. XML.
the xml file will have the same name as the catalyst profile you saved. right click and hit edit.
<Feature name="FanSpeedAlgorithm_0">
<Property name="FanSpeedAlgorithm" value="Manual" />
</Feature>
<Feature name="FanSpeedRPMTarget_0">
<Property name="Want" value="0" />
</Feature>
<Feature name="FanSpeedPercentTarget_0">
<Property name="Want" value="65" />
Change the value to "manual" and Want value to "65"
Save the file then reload your profile in catalyst.
65% seemed perfect for me, 70% was loud but you may need it if your case has poor air flow.
You will have to select the profile everytime you start the computer,
but it will work until there is a fix or better info so i can figure how to change the auto target temp.
Good Luck ,bretware