Noisy Hard Drive (ever since I obtained computer)

My Dell computer at work is fantastic - and very quiet, even when I start or close programs. I've had a Dimension 4700 at home for about a year, and the 120 gig hard drive is very noisy (even as I type this post). It's frequently making loud disk accesses, even when I'm not doing anything, which are very annoying. Why can't my home Dell be as quiet as the one at work? I think I know the answer - my home PC has a bottom of the line hard drive.

I have a 300 gig Maxtor external drive and it's extremely quiet. I bet a Maxtor internal hard drive would be the same.

I've have many .AVI files files get corrupted - contaminated with white static, have lost a key file needed by my Netscape internet program, and now have some key files messed up in my Norton Antivirus program. I want to get a new hard drive, but the Dell bureaucracy doesn't offer much support - they say with a year depreciation, my current drive wouldn't be worth much anyway. Seems like the most efficient thing to do is go down to CompUSA and have them install a new Maxtor drive and reinstall my basic Windows XP and I'll take care of the rest of the programs myself. If I do this, does it void my 3-year warranty (not that the warranty is worth that much anyway!)?