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I have two external hard drives that, when left idle for a certain amount of time, will begin a flurry of activity. So far I've been unable to find any culprits.

I've been going through the post here: What is causing hard drive grinding?

I've tried both Process Monitor and Process Explorer but they don't seem to turn up much. This may admittedly be my own fault for not entirely knowing what to look for, but I could not find anything obvious that was accessing the drive at all.

I have two hard drives that take turns doing this and they have done it when connected to two separate laptops, as well. Any advice? What are some common causes of heavy background disk I/O that I could check for?

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Your antivirus software may be performing a scan of the drives. For example, Norton Internet Security is typically configured to perform scans automatically on idle.

Otherwise, Windows may be performing a background operation, such as defragmentation, on the hard drives.

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Thanks for the reply! I've manually disabled the drive in my antivirus, as well as enabled history for the Win7 Task Scheduler. My prime suspect is, as you suggested, the default defrag task since it has run recently. – Ryan Mar 27 '13 at 20:45

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