Yep, it's pretty hard to find anything with sound that doesn't violate somebody's rights. Much classical was written long ago, so it's rare to find anyone alive who can legally claim rights to it. One can sell a recording of a performance of the material, but that doesn't give them rights to it. It's like you can make a copy or photo of a 200 year old painting to sell, but it doesn't give you rights to it.
I thought I got all the permissions proper to run a low bandwidth version of a movie there for a limited time only. So when I start running the movie there, I get a notice that I don't have permission for a song in the movie, "I want to break free". Golly, when I get permission to temporarily run a low bandwidth video, I thought that meant with the audio of the video too. For now, I had to give permission for Sony, & some Irish recording company to run ads there, to temporarily be allowed to play the movie with the audio.
Also in the movie, there's a point where just 4-5 seconds of a song (Where the referee shows up on the field), "All the right stuff" plays very faintly in the background. If you're not paying close attention, you probably wouldn't notice any music playing in that spot at all. But their copyright software found it & I had to get permissions for that damn song too by letting them run ads there too! I use ad block so never see the ads anyway.
That's why I stopped running ads here to help support Betty's. Hardly anybody ever clicked on them. About 95% were using ad blocking software so never see the ads (just a big ugly blank space where the ad would be), & the other 5% almost never notice or click on them. So it was a lot of daily work managing the ads, & clutter on the sites, to just earn $3-$10 a month. In the general population a lot of people don't have a clue about ad-blocking, but because it, & all things computer are discussed here, almost all our users are using some kind of ad blocking software.
Currently working on a astro-pix slideshow. I'm using sounds, & audio effects made at home on my computer to get around paying for rights or having a ton of annoying ads over the video to cover the rights.