I get this on my Thinkpad T60, Radeon X1300 running debian sid.
As well as crackle on the internal intel audio, I get even worse crackle and popping when using my Logitech V20 USB speakers.
The only thing that resolves the problem for me is:
echo mid > /sys/class/drm/card0/device/power_profile
But then gnome-shell and all 3d apps are really slow.