Just because you can find something on the on the web doesn’t mean you have the right to use it; crediting a source isn’t always enough. If you want to use third party audio, you'll want to seek permission from the material’s source/owner (who may require a credit) or to make a judgment that permission isn’t required under the “fair use” doctrine of copyright law.
Fair use is addressed in Section 107 of Title 17 of the U.S. Code, which covers copyrights. The language is intentionally ambiguous, leaving it open to case-by-case interpretation:
Section 107 contains a list of the various purposes for which the reproduction of a particular work may be considered fair, such as criticism, comment, news reporting, teaching, scholarship, and research. Section 107 also sets out four factors to be considered in determining whether or not a particular use is fair.
- The purpose and character of the use, including whether such use is of commercial nature or is for nonprofit educational purposes
- The nature of the copyrighted work
- The amount and substantiality of the portion used in relation to the copyrighted work as a whole
- The effect of the use upon the potential market for, or value of, the copyrighted work.>>
This applies (and is not exclusive) to sound from news organizations, television shows, movies and songs. If you have any doubt about whether something is a potential fair use violation, the best practice is to not use it.