I am not a hardware expert, this is just based off of some experiences I've had:

Have you blown out the dust of your PC with compressed air? (Make sure you don't accidentally blow the dust deeper into crevices)
If enough dust builds up, the heat might not vent properly, causing the fan to turn itself on higher, making the whirring noise.

Also, I bought a videocard a few years back - after about six months, it started getting really noisy. Turns out, the seal around the fan was defective (or something), and the oil/grease around the axis of the fan dehydrated, so the fan was whirring extra loud (and wasn't working as effectively) because of the friction from a lack of oil. So I take apart the card (voids the warranty) and oil it with standard machine oil whenever it starts sounding really loud (every 3-5 months). It's last me several years now, I've probably re-oiled it 10 or more times. I blow out the dust in the case whenever I'm re-oiling the card, just to kill two birds with one stone, though the dust doesn't build up too much in only 5 months.

The overheating videocard (because of dust and the lack of oil) caused computer shutdowns in the middle of online FPS gaming sessions (a safety precaution when the card gets too hot, to prevent it from being damaged).

"Guys, seriously, dust caused my computer to crash!", "yea whatever d00d. way 2 abandon your teamm8ts!"

I'd just blow out the dust before proceeding further, and update your graphic driver while you're at it.

What Servant said. I've clean several machines that would run okay (you could hear the fan, but only just) and when the machines would actually do something intensive, the fans went crazy. Just blowing the dust out of the fans eliminated the loud noise from the fans.

I am not a hardware expert, this is just based off of some experiences I've had:

Have you blown out the dust of your PC with compressed air? (Make sure you don't accidentally blow the dust deeper into crevices)
If enough dust builds up, the heat might not vent properly, causing the fan to turn itself on higher, making the whirring noise.

Also, I bought a videocard a few years back - after about six months, it started getting really noisy. Turns out, the seal around the fan was defective (or something), and the oil/grease around the axis of the fan dehydrated, so the fan was whirring extra loud (and wasn't working as effectively) because of the friction from a lack of oil. So I take apart the card (voids the warranty) and oil it with standard machine oil whenever it starts sounding really loud (every 3-5 months). It's last me several years now, I've probably re-oiled it 10 or more times. I blow out the dust in the case whenever I'm re-oiling the card, just to kill two birds with one stone, though the dust doesn't build up too much in only 5 months.

The overheating videocard (because of dust and the lack of oil) caused computer shutdowns in the middle of online FPS gaming sessions (a safety precaution when the card gets too hot, to prevent it from being damaged).

"Guys, seriously, dust caused my computer to crash!", "yea whatever d00d. way 2 abandon your teamm8ts!"

I'd just blow out the dust before proceeding further, and update your graphic driver while you're at it.

+ Dragonsoulj

Sure, I do that every 4 months or so. All components out. Anti-static wrapping. alcohol, cotton buds and tissues. :)

And I do grease my fans from time to time, but they still make whirring noises. :)

(I'm really picky with the internals not getting layers of dust on them)

I do need a qualified method for cleaning the fins on my heatsinks, though. Compressor air doesn't always do the trick.

At least at 90 psi, and I'm a little scared to break my hardware...

The noises were produced by my ICs while the fan produced constant humming and and my Slave HDD slept quietly,

so I'm convinced it's not due to mechanical components. As i stated, I've had the experience(as in I didn't pay attention to other comonents before) with my GPUs earlier,

and recognize CC Ricers and Olof Hedman's noise GPU phenomenon. So I'd say Brother Bob was right with respect to the specific case I wrote about...