HDD makes loud clicking sounds

hi,

Download hard disk sentinel trial, it will show you if the drive is failing.

If you already have a fresh backup, wait for the drive to die (or not), then replace and restore if needed. If you don't, now's a VERY good time to make one. Get an external drive at least as big as your disk capacity and create a Windows System Image backup (search backup in Control Panel; if you have Windows 8.1 it's still there, just hard to find).

Clicking sounds from drives are due to read head movement. Could be drive fragmentation making it rattle more, could be you shifted the drive in the case so it amplifies normal clicks a bit, could be impending disk failure. Since you described it as VERY LOUD, I'm guessing the last one.

When a consumer drive fails to read a specific region on the disk, it does read retries. After a few failures, some firmwares try to align the read heads mecanically... by slamming them against a stop on the side of the drive housing. I think this is what you're hearing.

You can check what the drive thinks about its health using HD Guardian. Open it up, hit the "Manage' tab, and select SMART Attributes.

The best* predictors of failure are:
Current Pending Sector Count: damaged areas of the disk that cannot be read. If you try to write data here, the drive will re-map it to a spare region and mark this one as un-usable.
Reallocated Sector Count: number of regions of the drive that were remapped

Non-zero counts for those are bad. If either of those numbers starts going up, your drive is more likely to die soon. You want rough statistics? disks with >1 reallocated sectors or >2 pending sectors had about a 70% survival rate at 8 months, vs a rate of around 97% among all drives (I'm eyeballing that off a graph -- don't come after me with pitchforks if I'm off a few %).

*Even the best predictor isn't very good, according to Google's disk failure study. The tl;dr is, SMART errors are only found in ~50% of failed drives, and while Reallocated Sector count is the best predictor of failure, it's still bad. Drive survival is better than you might think -- even for 2-year old drives experiencing a reallocation, survival was 60% of the population at 8 months. See the graphs on page 9.