External hard drive duplicates too many times

Hello,

I've been having a problem with an external hard drive I have (Toshiba).

I have an external hard drive as a Time Machine, no problems there.

But I have another EHD, only plugged when I need to find a file on my backups. Sometimes, I forget to unplug it and I turn off my iMac, and the next time I turn it on, I obviously forget the EHD is plugged, so when it's loading the desktop, the external drive duplicates at least 50 times on my desktop.

I try to eject them all, but takes a lot of time, so I shut down the computer, unplug the drive and then turn it on again. To check that everything is ok, I replug the drive, and it comes with problems, like a Damaged Folder included, but the files inside it are not specific on which files are actually damaged. I have to repair the disk and mostly all the time I have to format it, and then again it happens again if I leave it plugged and turn on the computer.

I have used an application to recover my files, but I have lost a few because of this weird behaviour.

I want to know if someone knows what's going on? If it is something on the EHD, or the USB, or my iMac.

Many thanks.