external hard disk does not spin down

I've had this issue since an update 1-2 months ago. I can no longer spin down my two external hard disks with "sdparm -6 -f --command=stop". In fact, by feeling the drive itself as I issue this command, I can tell that it spins down momentarily (for less than a second) before spinning up again. Is something polling external hard drives? "killall hald-addon-storage" did not help. I see /usr/lib/gvfs/gvfs-hal-volume-monitor is running, no idea what it does. Could that be it? This was not an issue a 1-2 months ago.