Sound coming from harddive when starting up

When I start up my computer right as I turn it on, my harddrive makes a weird sound.

It sounds like a hollow tapping.
It's a series of 4 taps, and it happens 4 times in sequence, and then not again.

EDIT: It sounds like a very quiet version of http://www.thenetworkadministrator [...] ge%203.wav that click, but not following that pattern.

Both times I powered up, it was a series of 4 quick clicks, 4 times. After that it doesn't do it again until I power down again.

It's within 1 second of powering on and not anymore after.
However, today was the first time I ever heard it do that.

Though, if you have an example sound clip of that, I could tell you if that's what it is.

(Either way, I ordered another harddrive and will clone this one over)