This was put in the actual files by the encoder. Check the “Description” field in your library of music files. I’ve also found weird tags in the comment field as well. I had to do this to my entire collection, I ended up just writing an opus script to just clear that field out.

You will need to refresh your collection to reflect the changes and those “ads” should be gone.

The ad is coming from inside the file! Look at all the extended tags using a tag editor. I usually use puddletag