hard drive - Is my shift hitting the fan?

On my laptop, an odd problem has developed. Whenever I press my left shift key, I hear a funny high-pitched sound like something is spinning against it. No other key causes the effect. Is this likelier to be the fan, the hard disk (ulp!) or something else?

EDIT: Oh, sorry I didn't specify! My computer is an Asus U46E-BAL7.

As it happens, the problem somehow went away in the twelve-plus hours I've been away from the machine. I'm guessing ultrasawblade's guess was basically right; some detritus underneath the key could have been partly blocking the fan, causing the fan noise's pitch to change when the key was pressed. It's hard to imagine what else it was unless the CD/DVD drive was invovled.

Is this likelier to be the fan, the hard disk (ulp!) or something else?

Since hard disks don't expose their platters, and there isn't anything else with moving parts in a laptop, it has to be the fan. Your laptop would probably stop immediately and not boot afterward if you were pressing hard enough on it to cause the head of the hard drive to hit the platter.

You may try dusting out your laptop's vents with some canned air - it could be that you're pushing some dust around in a weird way.