If the hard drive in your computer is typical, it makes a distinctive sound that probably learned to recognize once you had used your computer for a day or two.
The sound coming from your hard drive might be a quiet, smooth hum that you can barely hear or a slightly louder thrashing sound, but whatever sound it makes it should make consistently with little deviation.
If you begin to notice an unusual whine or clunking sound coming from your hard drive, take notice. Odds are the drive is about to go belly-up soon and take your programs and data with you. You do have a current backup on hand just in case, right? If not, you need to create a backup image right now because the drive could fail at any time.
The easiest way to deal with a failing hard drive is to replace it while it’s still working. Simply buy a new hard drive, temporarily install it as a second drive, clone the old hard drive’s contents onto the new one, then remove the old drive and set the new drive as the primary boot drive in your PC’s BIOS settings. And I recommend that you do it quickly before the old drive dies on you at the worst possible time.