XPS 410 Hard Drive Clicking at Startup

I have a Dell XPS 410 that I purchased in January 2007.  I have upgraded the RAM to 4 GB (4 1GB sticks) and I upgraded to Windows 7 Home Premium 32-bit when it came out in '09.  Other than that, nothing else has been changed.  About two weeks ago, my hard drive started "clicking"  when my computer starts.  It does not exactly sound like the "click of death", but more like the sound the computer makes when it turns on and off.  When I turn on the computer, it goes to the Dell start screen and clicks 6 times, pauses for a few seconds, and clicks again twice and pauses again.  Then the computer boots as normal and seems to work fine.  It does take up to a minute to access files and programs once I get to the desktop.  I am positive it is the hard drive, as I have opened the case and held the hard drive in my hand while the computer boots, and I can feel and hear the click from the hard drive.  I usually turn my computer on in the morning and leave it on all day if I am going to be at home.  The strange thing about it is that it only clicks like this when it is "cold," meaning that the computer has been turned off for several hours and has cooled off.  Simply restarting the computer or turning it off for a few minutes does to duplicate the problem.  The hard drive has passed the Dell F12 test and the Western Digital test.  As suggested by Western Digital, I have removed the data cable and then started the computer to see if it could be the data cable.  It exhibited the same symptoms, so it is not the data cable. 

I am pretty sure my hard drive is dying, but it is strange that it continues to work.  I have backed up all my data in case it dies.  I do not plan to replace the hard drive,as I had already considered buying a new computer before this started.  Does anyone have any idea what could be the problem?  I have heard that a power supply could be the issue, but I'm not sure how to check that.  I like to get 5 years out of my computers, so I'm close to that.  I'll use it as long as I can.  I'm sorry for the long post, but I wanted to give all information possible.  Please let me know if you have any idea what this could be.