This solved the issue, thanks. Can I suggest adding a note to the settings screen to help others? Also, for anyone else reading this thread, the fix is about login behaviour. If you test this by quitting USBClean and then launching it again (as I initially did), the window will still open in that case. It seems to specifically stop the window when the app launches at login (which is fine). I also found that, by uninstalling USBClean and then reinstalling it, it no longer shows under the 'background' section of the Login Items in System Settings.