Removable disk cannot be removed

I am running Windows 8.1 & recently noticed that I have 4 removable drives listed in Windows Explorer that do not exist. They are all generic with names Compact Flash, MS/MS-PRO, SD/MS-PRO & xD-Picture. I realize that they are likely from devices I ran once through my USB port but I really don't even know what they refer to. EG: what is xD-Picture? I want to get rid of them & have removed them using disk manager but they keep coming back.
I was not able to find anything on TSG that referred to my problem.
Help!