Interesting… YouTube is now disabling the audio rather than removing the entire video (where the audio copyright is in dispute or there are infringements).
The notice says: “The video contains an audio track that has not been authorized by [name of music publisher]. The audio has been disabled. More about copyright.”
Here’s a screenshot of the notice (click on the image for larger size):
(I took the screenshot from this video I stumbled upon.)
I’d suggest YouTube could go one step further: suggest or direct the YouTube user to sites like ccMixter for suitable CC licensed materials.