2008 Sonata Aux Cord Install, Very quiet

[BrokenWrist]

I just completed this install - http://xmtoaux-insonata.blogspot.com...your-2008.html
In which I had "replaced" my XM radio with an aux cord. I got everything to work fine and I can hear music from all of the speakers.

However, even with my iPhone and radio set to FULL volume the music is still very faint, I can hear the music but it is quiet and staticy. I've tried everything I know plus what is mentioned in the comments of that article I linked.

Does anyone know how I can fix this issue?
or/and Would anyone recommend I do something different?

TIA