I came across some free titles from Audible in my wanderings this morning (don't remember where though, apologies to the site that posted the links!). Five of them supposedly feature a soundtrack that includes music and sound effects designed to enhance the listening experience and Audible will supposedly send a follow up survey for feedback.
Curiously, I already had Outlander in my library yet it let me purchase this version, too, and sure enough, I now have two versions of Outlander in my Audible library.
Not sure how long these will be free...
Outlander by Diana Gabaldon
http://www.audible.com/pd/Romance/Ou...ook/B003TFYOL4
When You’re Ready by J. L. Berg [Soundtrack Edition])
http://www.audible.com/pd/Romance/Wh...ook/B01M22DMKN
The Turn of the Screw [Soundtrack Edition]
http://www.audible.com/pd/Classics/T...ook/B01MA1MLST
The Innocent Ones [Soundtrack Edition]
http://www.audible.com/pd/Mysteries-...ook/B01M3NPV71
Jane Carver of Waar [Soundtrack Edition]
http://www.audible.com/pd/Sci-Fi-Fan...ook/B01M61UFMG
The Wind in the Willows [Soundtrack Edition]
http://www.audible.com/pd/Classics/T...ook/B01MF4WPSC