While it's true, that if no money is involved, there's less likely a chance for copyright infringement to be enforced, the owners of that same song/lyrics/snippet may object to its usage. Copywrite legal fine print always says things about not reproducing any portion of this book/article without express permission. Try writing some fan fiction of Anne Rice's characters (as well as some other well-known authors) on a public forum, even for free, and you may find a cease and desist letter in the mail.
It's best to tread carefully and seek out permissions where appropriate, or not use things that aren't of your creation in the first place if you can't be sure.