I'm running Ubuntu 11.10 on an Acer Aspire One 722. Whenever I'm on battery power I get a clicking sound from my hard drive every 5 seconds or so (this does not happen when the laptop is plugged in). I'm dual booting with Windows 7 and I don't get the clicking sound in Windows.

The clicking sound stops when I run the command:sudo hdparm -B 254 /dev/sda

Also, according to:sudo smartctl -H /dev/sda my hard drive is healthy.

Is this clicking sound something I can just ignore? Or is it a serious problem and will it eventually damage my computer? If so, how would I fix it?

I have tried adding hdparm -B 254 /dev/sda to my /etc/rc.local file, but I still run into the clicking problem if my computer boots while plugged in and is then unplugged. Also, I'm finding this fix to be unreliable. Sometimes it works, sometimes it does not. Is this a good solution and is there a better way of doing this? Also, would running my laptop with a -B value of 254 have any negative effects? (I read somewhere about a lower level protecting the hard drive from bumps)