What's up with that?

[gangof4]

I just installed a LaCie d2 Quadra Hard Disk to my iMac to use with Time Machine. It's backing up every hour, but every 15 minutes or so the drive clicks softly as the blue light flutters for a sec (seems like it's reading something but in between scheduled backups when there is no other activity going on.)

Is this normal?

 

[rufwork]

Sorry, based solely on the title...

That was worth it.