Older Dell Dimension that I upgraded with two new hard drives. Started humming at startup before I did the upgrade. Thought it was the main fan so I replaced it. Still hums. I press start and immediately it kind of "groans" for a minute until it's booted up and then it's gone. I think I read somewhere that it's the hard drives "getting up to speed" but that doesn't sound right, does it? Any ideas? Thanks, V.