Can I add MP3 background music to my 360 virtual tour?

Yes, you can do it with a Pro Account or a Gold Account which allows you to add background music or even add a voice track in MP3, in order to guide the visitor and to provide a complete immersion.

Music / MP3 will need to be created on your end or be royalty free. Here is an example amongst others: https://www.auboutdufil.com/index.php?tag=ambient