Failed hard drive trying to mount

I have a 2010 iMac and had an additional SSD drive fitted internally a few years back. This SSD runs High Sierra and the original drive was used for storage.

Now, the original hard drive has failed. I get an alert saying "The disk you inserted was not readable by this computer. Initialize/Ignore/Eject". None of these make any difference once the Mac goes into power save or sleep mode. I get this sound of the disk attempting to wake itself, spinning until it gives up.

Other than this issue, the iMac, whilst very old indeed works fine for the use it gets.

Is there some help I can get to stop it trying to revive this old disk? Happy following Terminal instructions if this is how to do it.