Noise from Caviar Blue

I have a noise problem with a new WD5000AAKB PATA Hard Drive that i have just purchased.
The problem is that the drive is constantly making a clunking noise when it is idle.
I first noticed the noise some hours after the drive had been povered on the first time.
The clunking noise occurs with an interval between a few seconds and a minute and only when the drive sits idle.
This is the second unit that exhibits this irritating noise. The first one i got had the same noise problem, but only worse and I therefore had it replaced.
The noise is very annoying and i find it unacceptable and unbearable to listen to.
I have newer before heard such a noise coming from a hard drive.
I have run a WinDlg quick test and it came out ok.
How come it is making this noise and is my drive defective in some way?

I am running Windows XP SP3 and the drive is partitioned in two parts. C: with 25GB and a E: with the rest.

I have recorded two audio files to let you hear the clunk noise it is making.

http://www.mediafire.com/file/99cv9za2be9w22p/Clunk1.wav

http://www.mediafire.com/file/3piyz896meozglz/Clunk2.wav

Hello,

I was able to find two WD articles regarding drive noise. See below:

http://wdc.custhelp.com/app/answers/detail/a_id/568/session/L3RpbWUvMTMwNTY0MDc2MS9zaWQvNFFuZiphdWs%3D

http://wdc.custhelp.com/app/answers/detail/a_id/61/session/L3RpbWUvMTMwNTY0MDc2MS9zaWQvNFFuZiphdWs%3D