I had something similar, where the computer would consistently hang for a second or two when the frequency was lowered. My fix was just to manually set the 'performance_governor' to 'performance' or 'powersave'. Some old notes: http://www.ii.uib.no/~ketil/ubuntu-prob.log
-k -- system pauses https://launchpad.net/bugs/64474 -- ubuntu-bugs mailing list ubuntu-bugs@lists.ubuntu.com https://lists.ubuntu.com/mailman/listinfo/ubuntu-bugs
