My computer occasionally bogs itself down for no reason (best I can tell)

I've got 4 hard disks (1 system, 3 storage) that are varying degrees of full from 25%-85%. Occasionally, my system will just bog down and I can hear what sounds like a hard drive winding up or something and my system locks up for maybe 5 seconds and then I can use it again. This seems to happen most often when I am opening or scrolling through a large database (it happens in Windows Explorer, J. River Media Center, iTunes, Windows Media Player, several other applications)

My install is fresh Win7/64 bit. I've got 7200rpm drives, a decent video card, 8 gigs of RAM, a quad core processor, etc. etc. so there's really no reason I can think of why my system would be jamming up... especially when all I use my computer for is very basic things (email, media playback, internet, occasionally MS Office)

Any ideas?

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