What's up with my hard drive?

[gangof4]

I backup my imac hourly via TM to a LaCie 1TB external hard drive. However, at different intervals between scheduled backups my drive clicks on and the blue light flickers as if the drive were reading or writing something. What's up with that?

 

[satcomer]

If you used Time Machine it is set to write changes every two hours. You can see this and change the interval by using TimeMachineEditor. Plus consider getting the Dashboard app Time Machine Buddy.

 

[gangof4]

Understand Satcomer, but why is my drive kicking in 20 minutes after the last backup and 40 minutes before the next?

 

[-tWv-]

Maybe spotlight is indexing it? I have no idea