Time to boost the signal! This September I am planning on doing a roundup of some favourite resources for Table Top Role Playing Games. Most of which are free and online.
Resource Spotlight: Free Music Archive
|"Piper" by OpenClipart-vectors
The Free Music Archive is a collection of free and royalty free music you can download and use in your creations: some with and some without music. Most of it is under Creative Commons, and it is advisable to check whether a piece requires attribution.
Note: I personally have run afoul of a predatory company that has persuaded several of the contributors to monetize their work. These companies will put false strikes on content uploaded to platforms like YouTube in hopes of intimidating you into paying a fee. This is a small percentage of the content, and should be reported.
If you are looking for sound effects, Orange Free Sounds is a similar service for sound effects.