If its a Desktop, decrease you dirty_writeback_centisecs to 3 seconds (or less but not lower than 1 second)
echo 300 > /proc/sys/vm/dirty_writeback_centisecs
If its laptop... you want to only do that should you be plugged in.
If its a laptop change it to 15 seconds when on battery.
I know that Ubuntu has been playing with "standard" numbers on trying to be GREEN. You might have it up there already. My Debian installs all have it at 5 seconds (500 centisecs)