Mint Mate 19.3 opening external hard drive volumes in Panel at boot up

No luck finding this elsewhere on the 'net. For some reason suddenly the three volumes "F", "G" and "H" that reside on a Seagate 1 Terabyte external USB drive started to appear in the Panel when the system boots. I don't think (could be wrong though) I did anything to cause this.
The same volumes have always appeared on the desktop. Closing the volumes in the Panel does not affect the function of the desktop icons. No drives or volumes are listed in "Startup Applications". How can I make this go away? Thanks.