Yes you don't need to do the heroic mission you can just walk to the area in patrol. I have hear one of three things that may be required to get this though 1. You're playing with your original D2 character. Think this means the first guardian you started the campaign with. 2. You have done all the heroic missions on Titan before. Possibly why you're seeing Siren Song as you may not have done it heroic? 3. It's the Guardian you did Rat King with....... yeah this one sounds far fetched but just throwing it out there.