HD likely dying, need to backup OS

Hello, About 8 months ago my husband purchased a Dell Inspiron laptop running Win 7. A few days ago, the hard drive started...well, not exactly grinding, but making a sound like a noisy fan - but the sound is coming from where the HD is located. It makes the sound intermittently. We're probably just going to replace the HD rather than send it away, even though it should still be under...