Help me diagnose hard drive problem—link to audio

I upgraded the hard drive in my 12" PB the other day, and now I've noticed it makes a funny sound. I need to know if it's a bad hard drive, bad installation, something serious, etc.

I recorded audio of the sound (with external mics), and posted it here, It sounds like a swallow, or a drop of water hitting an empty bucket. It happens once every 5-20 seconds, and does not occur when the hard drive is in use (for example, it didn't make the sound when recording in GarageBand—I had to use a different computer to record the offending sound).

It is a Western Digital ATA 120GB 2.5" drive.

Is the drive bad? Would I have better luck with a different drive? Different brand? Just opening up and reseating it and hoping for the best?

I certainly don't want a faulty drive, but I really don't want this damn annoying sound... it's clearly audible in a quiet or semi-quiet room.

thanks!

sorry for the bump

I have to replace this drive, because no way can I live with an annoying little swallow noise every 10 seconds. I'd still like an opinion, however, about whether this is a typical problem, specific to this manufacturer, do to my installation error, or whatever you can tell me.

anyone?