Let me help you on this one!
I remove rhythmbox from every install I do of zorin os, but I reinstalled (and searched online) to see where the config files were. And, here is your solutions!
rm ~/.local/share/rhythmbox/
rm ~/.cache/rhythmbox/
rm ~/.gconf/apps/rhythmbox/ -r
If the third command fails (not found), you'll have to replace every gsetting, copying and pasting every line of these, one at a time.
gsettings reset-recursively org.gnome.rhythmbox
gsettings reset-recursively org.gnome.rhythmbox.display-page-tree
gsettings reset-recursively org.gnome.rhythmbox.library
gsettings reset-recursively org.gnome.rhythmbox.player
gsettings reset-recursively org.gnome.rhythmbox.plugins
gsettings reset-recursively org.gnome.rhythmbox.plugins.iradio
gsettings reset-recursively org.gnome.rhythmbox.plugins.lyrics
gsettings reset-recursively org.gnome.rhythmbox.plugins.magnatune
gsettings reset-recursively org.gnome.rhythmbox.plugins.replaygain
gsettings reset-recursively org.gnome.rhythmbox.plugins.visualizer
gsettings reset-recursively org.gnome.rhythmbox.podcast
gsettings reset-recursively org.gnome.rhythmbox.podcast
gsettings reset-recursively org.gnome.rhythmbox.rhythmdb
gsettings reset-recursively org.gnome.rhythmbox.sharing
gsettings reset-recursively org.gnome.rhythmbox.sources
gsettings reset-recursively org.gnome.rhythmbox.plugins.alternative_toolbar