You probably have a few dozen duplicate files, chiefly MP3 and photos in the Google Drive. This https://softgateon.herokuapp.com/drivecleaner/ is a handy tool that scans selected directories and finds any duplicate files inside them. The app works with all sorts of files and can also be configured to scan sub-folders within a given directory. It supports IE10+, Chrome, Firefox… even provides a connection with Google Drive. You can directly scan duplicate files with your drive.
For Chrome users, here is it as a Chrome extension: https://chrome.google.com/webstore/detail/duplicate-file-finder-cle/bkefnddmfngncidpmibnleniddiopejg