Yes - but you have to create an account with Soundcloud first. Anything you upload to Soundcloud must be marked as "public" when you upload it. After you upload a track and make it public, click on the "Share" link to find the exact web address the track is stored at on Soundcloud. Copy that address and then once in Roll20, search for the copied address...it'll take you right to the specific track. Legally speaking, since you're uploading a file to the public, you need to make sure you have an appropriate license or rights to do so.