echo on audiobooks on ipod 4

I have downloaded two audiobooks from audible.com. They play fine on my macbook pro and on my iPad 2. My ipod touch however has an awful echo. I found an old thread about this, but the recommendation applied to older ipods. I contacted audible and they were very nice and told me the first book was marked as vintage so they gave me another one (both by Terry Pratchett in the discworld series). I tried resetting my ipod and that did nothing. Any ideas?

thanks,

Joe