@crl also, do you hear unusual noise coming from HDD? If you hear loud noise (e.g. clicking), it means you have little time for doing backups as HDD is dying. Also failing HDDs can get hot faster* so add a little cooler for controlling heat.
*caused by friction, vibration, voltage issues etc.
Remember, HDD is the most heat-sensitive part of your computer (max allowed temp. is about 55-65*C, usually/sometimes not cooled at all)