I thought I'd try a google search for "harddrive lubrication" (safe search on!!).
Came across this gem:http://www.bbspot.com/News/2004/05/bbspot_labs_whining_hard_drive.html
At first it almost look feasible (almost, except for the platters setting on the desk next to the drive) until it got to the part about greasing the platters... DON'T TRY THAT, IT'S A JOKE!!!
After a quick search I stand by my previous answer. If you had everything backed up and wanted to take a chance, I would think silicon to be best, but I wouldn't ever try it unless I already had my backup plan in place and my new hard drive copied already.