ok so ive had my imac since 2009 and one sooo annoying thing that happens is it will randomly hang, with the rainbow beachball and spin up my usb harddrive before it will proceed at what im trying to do. it does this with any external usb harddrive i attach -_-

With the weirdest apps too, Preview, Xcode, iTunes, Safari, Photoshop, etc

Am I'm pretty sure I don't have anything system wide important on the usb drive but some reason my iMac decides it needs to spin it up to proceed

Happened on Snow Leopard 10.6.3-.8 and Lion now.

Weird? or Normal?