Technically, there may be no errors found on the drive but if the mechanical parts are starting to fail, it will continue to make noises when it's working the hardest.. It doesn't work as hard in Safe Mode.. Your best bet is to make a backup copy NOW, then replace the hard drive and reinstall everything using your recovery discs.
Hope this helps.
My hard drive when booting up normally will click click scratch 3 minutes or so after the start-up screen. Normally i know its the sign of death. But i was wondering could it still be a bad sector if it still works fine in safe mode. Also Disk checking doesnt find any errors with it.