Suddenly noisy drive

I was adjusting my BIOS settings the other day, trying to tweak some more performance out of my system.  When I was done and rebooted, I noticed that my previously almost silent hard drive (Western Digital Caviar Black) was suddenly fairly noisy as it chattered during R/W operations.  Could I have done something in BIOS to affect the drive, or is this just a coincidence?  Does sudden noisiness in a hard drive indicate it is about to fail?  I’ve only had the drive for about 6 weeks.  I also noticed in an entry in your FAQ’s that enabling AHCI and then rebooting won’t work because Vista doesn’t have the right driver, but then it said that you would have to rebuild the system if you did that.  I did this as part of my BIOS experimenting and was able to put the settings back and boot normally afterward.  Do I need to rebuild my system now?  Here is the quote from the FAQ’s.

Note: If you installed Windows in IDE mode (which means that you didn’t use F6 and supply a driver disk), then simply changing the BIOS setting to AHCI mode and rebooting will cause Windows to fail and will require a repair install. Most people are advising to reinstall Windows if you want AHCI enabled

I have run Data Lifeguard Tools for Windows on the drive and it ran the quick test clean, although I have not run the complete test yet.

Thanks for any help.

How much data are you caching to the hard drive? How large is your page file? If your using your hard drive really hard its going to be much noiser than if your using it with standard configurations.