Loud clicking noises from HDD

[SilverPrince]

Hello, I've got a Hitachi Deskstar 2TB HDS5C3030ala632 in a USB box with cooling.

A few days ago it started to make some loud clicking noises.
it happens when there is no access (or at least no copying or testing).
When it copies something - clicking stops. Then when it is finished - it starts again.
It's pretty loud and maybe 1 to 4 times a second and irregular.

I've tested for bad blocks with Victoria and HD Tune Pro and there are no bad blocks.
It's connected via USB to a notebook, so my understanding is that SMART reading would not be correct???

It has some important photos and documents. I've made a backup quickly.
But generally i'm quite concerned.

Do you have any ideas? Thank you!

[SilverPrince]

UPDATE- Here are the SMART results

[michael chiklis]

Very likely your drive has bad surface, many bad sectors were reallocated but many more could be still in pending status (even if SMART doesn't indicate pending sectors) or could be weak sectors around that can come damaged soon.
The reason why your drive is generating bad sectors could be due:

1) wear of the surface (hdd is too much used)
2) Your USB box controller is not working properly (or the power cable is damaged), if is this the case then unmount the drive from it and connect to sata port inside your PC.
3) Power supply of your usb box is faulty, if is this the case then unmount the drive from it and connect to sata port inside your PC.

[SilverPrince]

Thank you. I ended up buying a new HDD . And the data luckily is safe.
this one has already 1000 bad sectors and it's getting worse. ..