Actually, if you're hearing a clicking sound from the hard drive, that's more a sign of impending failure than anything to do with power settings. I would be taking this time to make a full backup of any important data, and then make sure you've got Dell's number so you can call as soon as the drive does fail. Assuming it's the one that came with the system.
When using Photoshop or watching video files, I will occasionally get OS freeze for around five seconds, then everything resumes normally. During the freeze I can hear the hard drive spinning up, and then a click sound before everything resumes. I'm thinking it may be something to do with the power settings? The settings at the moment are keeping almost everything running at all times, but I do still have the turn off hard disk after 20 minutes feature on. Should I turn this off? Will it reduce the lifespan of my hard drives if they're constantly running full power (I rarely shut down). Here are my specs:
Dell XPS 435MT
Intel Core i7 CPU 920 @ 2.67GHz 2.67GHz
Gcard: ATI Radeon HD 4800
64-bit Vista Home Premium SP1
Main drive: 750GB
Second Drive: 1TB