Software :: Hard Disk Keeps Spinning Down

For some reason my internal hard disk keeps spinning down (and back up always immediately) at what seems random times for no apparent reason, which results in a rather long pause in system response. For instance in the loading screen, when i hear what i believe to be my hard drive spinning down the loading bar (which would normally increase steadily) will stand still for about a minute or two and continue normally afterwards. This is the case for anything that needs to load, like when i'm starting itunes or any other program, if the hard disk spins down while starting up the program it will take a minute or two then start afterwards. Same goes for watching or listening to media, a slight pause will occur. I've also noticed that any commands given while in this "idle" state are stored and will execute afterwards. Like typeing a sentence. The problem started occuring after i got my used hard disk space over �100GB. The system suddenly started going really slow and with hitches, even tough the total capacity is 148,92GB. Simply deleting some data to put it under 100GB again resolved the speed and hitches, but then the the spin downs started to occur.

I've searched the internet for people having similar problems who've already gotten help but without luck. Since i think it's the hard drive i've used Onyx and Disk Utility to repair the permissions on my hard disk, which held the same results : the spin-downs cease after i do it, but every time i restart the spin-downs would simply occur again. Is there any way to solve this permanently? Utility : Bevoegdheden voor 'Macintosh HD' worden hersteld (Permissions for volume 'Macintosh HD' will be repaired.) Determining correct file permissions........