Comment # 31 on bug 77677 from Garrett

(In reply to comment #23)
> This might be a duplicate of bug 76837.  Does disabling dpm help?  Append
> radeon.dpm=0 to the kernel command line in grub.

Adding radeon.dpm=0 to boot params did not work.  I am sorry to report. On my
7750 card. HDMI sound is machine gun like, still in Openlec.