I ask because my back up drive has started buzzing and is no longer recognised when I plug it in.
As to how dead? Its a Samsun HD160JJ and it makes a somewhat ominous “buzz, buzz, buzzzzz-buzz, buzz, buzz, buzzzzz-buzz…” when it’s powered up. Does that sound like some sort of unrecoverable failure?
And yes, I’m aware that I should be backing up the back up. I was when my computer with a DVD writer died and using my back up with an external writer was taking a looooong time.
Well, I think you have your answer…
Now!
The real answer; If you want to spend some money you can have the data retrieved from the disks as long as they aren’t mechanically/magnetically damaged.
IOW, for a pro not to be able to retrieve data you have to smash the platters to pieces. Practically, if you’re trying to retrieve the data yourself, when the computer no longer recognizes the drive you may be SOL.
Sometimes you can take the case apart and see if there are any loose connections. You may have a drive powered by the USB port or you may have one that requires an external power supply. Trying new power supplies or cables may also be a remedy.
Not even that dramatic. The read head of my hard drive came down on and scratched all over the disc of my hard drive. I paid about a thousand dollars for a professional data recovery service to tell me that nothing was recoverable.
So, not a total loss, just depends how much I want to pay to get the data back. I think I actually have the HD from the computer I backed up in the first place, so my photos should be retrievable from that (it was a motherboard failure that killed off that one).
I’m trying to figure out if it’s the HD or the caddy that’s making the noise, but that doubt is probably just my wishful thinking. Oh well 
One thing that might work is to get another of the exact same drive, and use its circuit board to replace the old one.
If the drive is making funny mechanical noises, it’s probably not the controller board. This site indicates clicking noises to be a fairly common problem on Samsung drives, and that opening it up in a cleanroom and swapping out the heads may be the only fix. (ouch!)
The same site says swapping controller boards often does not work because of how modern drives map out the bad sectors and store that mapping on the controller board.