User blog comment:MMYP999/Q&A, Anyone?/@comment-34964696-20171029065400/@comment-27416494-20171030032236

Right, I should probably start by saying that this can only be done with the Source Editor, which you may recognize as the small [ ] icon that comes up under your user page's options bar. You can place the code wherever you want from that point, as long as you've copied it perfectly.

After that, the only thing left is to browse the website Soundcloud for whatever song you want to use, and replace the highlighted part of the code with a link to the song you're looking for.