Sony Vaio HDD is randomly buzzing

It is weird, It seemd like i never noticed it. But when i Start firefox or have more programs running at a time the hard disc seems to buzz, kinda high pitched not like the usually working sound of a hdd.

I thought my hdd was broken and sony replaced my old hdd with a new toshiba 160gig hdd.

But again... I hear this high pitched voice... seems like its appearing when the hard disc is working the least... doing small writing operations, could that be?

Its a Sony Vaio VGN CR32W

Sorry for messaging again, I just figured out, that the sound could come from the speaker as well right?

Since the right speaker was broken once, and I guess the hdd is located on the left of the Sony vaio...

But how come the speaker does do random buzzing when the hdd is wokring more?