Reduce fan speed of ATI GPU with radeon open source driver

Reduce fan speed of ATI GPU with radeon open source driver

I have a Radeon HD 6950 connected to two screens on a machine running
archlinux.
Recently I changed from the proprietary to the open source driver due to
dropped catalyst support. Unfortunately by default the fans are very noisy
by default - apparently the power saving mechanisms do not work properly.
I set /sys/class/drm/card0/device/power_method to profile and
/sys/class/drm/card0/device/power_profile to low. This seems to work
# cat /sys/kernel/debug/dri/0/radeon_pm_info
default engine clock: 800000 kHz
current engine clock: 249990 kHz
default memory clock: 1250000 kHz
current memory clock: 1250000 kHz
voltage: 900 mV
PCIE lanes: 16
Unfortunately it does only help a little with the fan noise. I also tried
dynpm which doesn't really seem to have an effect (possibly due to the
dual head setup).
Previously, with the catalyst drivers, I had issues with fan noise after
suspend, but I was able to use the "ATI Overclocking Utility" to reduce
both shader and memory frequency which muted the fans.
Also I have dual boot windows running and there is no issue with fan noise
in idle on Windows.