Car speaker issue with iPhone and AUX cable

[jsossamon]

I play Spotify on my iPhone 5 through an AUX cable to my car stereo.  I don't think it's always been this way, but when I play a track the sound is playing roughly 80% out of the passenger side speakers, with 20% through the driver side and almost zero bass through my subwoofer. 

This doesn't happen from my iPod or through radio/CD/XM built into my stereo. Any idea what may cause this or a solution? At first I thought my speakers may have busted but that is not the case.