I used to have HD4870 in CrossFire and there was a guide that show how to manually adjust the fan speed for both GPUs. I thought the latest Cat should fix it but anyway, you might wanna give it a try:
1. Turn ON Overdrive in the CCC and leave the clocks speeds at default.
2. Make a profile in the CCC (this will be your fan speed profile, you can have more than one)
3. Find and EDIT (via rightclick) the "C:\Users\USERNAME\AppData\Local\ATI\ACE\PROFILENAM E.XML" File
Find:
<Feature name="FanSpeedAlgorithm_0">
<Property name="FanSpeedAlgorithm" value="Automatic" />
</Feature>
<Feature name="FanSpeedRPMTarget_0">
<Property name="Want" value="0" />
</Feature>
<Feature name="FanSpeedPercentTarget_0">
<Property name="Want" value="XX" />
4. Change:
Automatic to Manual
The FanSpeedPercentTarget value (shown as XX) to the percentage you wish to use.
"FanSpeedAlgorithm_0"....... is the 1st video card.
"FanSpeedAlgorithm_1"....... is the 2nd video card.
EXAMPLE:
<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" />
and then scroll down and the _1:
<Feature name="FanSpeedAlgorithm_1">
<Property name="FanSpeedAlgorithm" value="Manual" />
</Feature>
<Feature name="FanSpeedRPMTarget_1">
<Property name="Want" value="0" />
</Feature>
<Feature name="FanSpeedPercentTarget_1">
<Property name="Want" value="65" />
5. Save the XML file.
6. Activate your profile(s) in CCC.