Danny are you sure, that you've got powered antenna ? In European i30 (>2009) there is passive antenna. I also installed aftermarket multimedia station and only needed to change the antenna pole for longer (now it is about 60 cm long). Antenna works without powering, it hasn't any amplifier. Reception is good.
Maybe adding voltage to non-powered antenna cause interferences ?
It is high possible that Phil is right, so try him advise.
Always you can change whole antenna installation for aftermaket passive (or amplified) antenna with long mast. And I'm sure that it will be good option.