I got an external drive doing the same thing. I looked it up and saw it is the "click of death". Sure enough, no files can be read or moved during clicking/knocking on this one.
I read that and started trying to transfer files. I slapped the top of it.
Basically, it starts clicking and then files no longer transfer over to another external drive for backing up. I slap the top of the bad one that is clicking again, and they start transferring after a few seconds to half a minute.
It does it again and i slap it again, it starts back up okay again.
I'm hoping I get them all transferred before the final breath.
It is like 24 gb of stuff. I had wiped it clean and started on it again saving files just a few months ago when it was fine. I just cleaned it up then to create new space. It's prob ten to 8 years old.