You also might try
1. Use the defragger which comes with Windows (2K and XP) to see if the drive still makes the same sound. This would isolate the problem to DiskKeeper Lite behavior, not the disk going bad.
2. I also think the suggestion (made above) to run the disk manufacturer's diagnostic utility an extremely good one.
3. Less likely to help, but should be checked: Are the BIOS, Windows, and the drive itself all on the same "wavelength" as to the access method (PIO, UDMA2, UDMA5, or whatever?). Are the 2 drives confgured "master/slave" or "cable select"? Is ribbon cable certified for access method (40 vs 80-wire cable)? Just some thoughts ....