It made funny metallic clicking noises (tink, tink, tink) after the system warmed up.
At first I thought it was the hard drive failing. So I backed up the hard drive.. waiting for doom.
Then I thought it was the Sudden Motion Sensor parking the hard drive.
To read more about the sudden motion sensor see this page on the Apple website. Even after I started and stopped the sudden motion sensor the "tinking" sound was still around.
Then to make sure after I turned off the Sudden Motion Sensor, I booted the Macbook Pro into Windows 7 and it still made the tinking sound. Even booting up it made the tinking sound.
Then I found the "Fix Your Macbook Pro like a Champ" web page.
After I removed the bottom cover of the Macbook Pro and removing the ground connector shown on the website. No more tinking sounds....