Unmounted disk drive mysteriously spins up

Hi,

I just bought a Samsung F1 disk for my 2008 Mac Pro. I was happy to find out that the drive is faster and much more silent than the one that came with the machine. I plan on installing Windows on the old drive and have that drive sleep while in OS X.

I have a firewire 800 drive that I typically unmount when not in use so that the OS will not try to access it and cause it to spin up and down all the time. This works perfectly. The same can, unfortunately, not be said about the "old" internal drive. After unmounting the drive, it immediately spins down as it should. However, after 30 seconds to a minute, the drive will mysteriously spin up again. How can this be? The OS should not be accessing it when it isn't mounted.

This annoys me for a couple of reasons. The machine is much more quiet while the drive is sleeping and there's also the fact that the sleep mechanism doesn't seem to behave the way it should.

Anyone experience anything like this?

Edit: Oh yeah, I tried resetting the SMC by unplugging everything for 15 mins to no avail.

Just wanted to update this. It turned out that istat menus was causing the disk to wake from sleep. Uninstalled it and everything is now fine.