First, backup that hard drive. And I mean now! That drive could die any minute, and when it does, it will cost hundreds or even thousands of dollars to retrieve your files–if the files can be retrieved.
Do a full image backup of the entire drive, including all partitions. EASEUS Todo Backup and Macrium Reflect Free are both free and either one will do the job just fine. You’ll need an external hard drive to back the images onto.
Both programs also have an option for creating a bootable CD from which you can restore the backup. Create that CD.
Backed up? Good. Now you need to determine if it’s the hard drive making the noise, or just a fan.
If the PC is a desktop, open it up, turn it on, and try to locate the location of the noise. If you can’t, find yourself a hollow tube–the cardboard one from a used-up paper towel roll works. Holding one end of tube to your ear, point the other end to various locations in the PC, especially towards the hard drive and fans. You’ll easily pinpoint the source of the grinding.
Laptops aren’t that easy. If you feel comfortable opening yours, use the desktop instructions above. Otherwise, try to determine the location of the fan and the hard drive from the outside. The fan is probably near a vent. Most laptops are designed to make hard drives easy to remove and replace. If you can’t find where the drive is located, check your model’s online manual.
Once you know where everything is, use the cardboard tube method described above.
If the noise is coming from a fan, and the PC is open, look for something obstructing the fan. Remove it if you find it. If the fan is loose; tighten it. Otherwise, replace it.
But if a fan is making the noise, and you’re not comfortable opening the laptop, bring it to a professional and explain the problem.
And if it really is the hard drive making the noise? Buy a new hard drive, install it, and restore Windows and your files from that image backup.