The hard drive makes a grinding noise The cause is?

The reason is most likely the drive is getting old or defective. It may be about to break down and die. Please make sure to back up all important documents, pictures, videos, mp3s to another drive before shutting down your computer.

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I'd try something else first. It may indicate simply that the poor drive is working overtime to find things among umpteen Mb of rubbish - files are not stored in neat sequences. Turn off all open applications except the system tools (Control Panel & the file mapping). Give the disc a thorough cleaning - delete all those gash temporary internet files, browsing history, cookies, data or application files you don't need or should never have kept anyway... Then run the disc analysis and de-fragmenting software accessible via "Control Panel" (assuming MS 'Windows'). This will find out if the disc needs de-fragmenting, and to what extent. If it does, set it running and leave it to its own devices. See if that helps - it certainly won't do any harm!