Nearly all of the tunes in the background of this show come from Kevin Macleod at incompetech.com. It really is a fantastic thing he is doing and there is a gazillion files to choose from in every genre imaginable!
Most if not all of the music is made available via a Creative Commons license, which means you can use it without paying a ton of money, as long as you give the proper credit. I do this at the end of each episode and also list the songs in order, link to incompetech and the license in the show notes!
I don't know if this show would really even be possible without the music. The music really brings out the emotion or tone of the story and makes it that much more engaging!
Do yourself a favor, and check out Kevin Macleod's awesome work at one the links below, and consider supporting him via Patreon. Countless people for years and years to come will be able to see their projects come to life thanks to his work!
Royalty Free Premium Music
Support Kevin via Patreon
Creative Commons License's
(example of what incompetech makes available)