Best answer by Mathis
Thanks for getting in touch. Please read our Creative Commons FAQ in our help center for more information (http://help.soundcloud.com/customer/portal/articles/243852-what-is-creative-commons-). Please note that this article provides basic information and is not official legal advice.
To search for Creative Commons tracks, perform a basic search on SoundCloud, and then filter the results by Sounds only. Then, filter the results again so that you can find sounds to use or modify commercially. Here's a screenshot to help point you in the right direction: http://bit.ly/14tM4j3
Please note that we strongly recommend getting permission from the creator who uploaded the track you want to use before using their sounds. If you fail to do so, it's possible that they will not approve of the use and ask you or us to remove the material from your project at a later date.
You can also read more about copyrights here: http://help.soundcloud.com/customer/portal/topics/39593-legal/articles - if you have further questions around this, please get in touch with our Copyrights team directly via our contact form (and feel free to let them know we referred you from the forum).
Hope this helps!