NYCdesignkid

Hi everyone!!
I know this topic has been discussed numerous times, but I can not find a resolution to my problem.
I finally installed my carputer,and have some feedback problems. We ran good rca cables with a 1/8" mic jack 'Y' splitter to rca to the rca inputs in the aux of the HU and at first there was a tremendous amount of static and alternator whine. So we tried a ground loop isolater, and this minimized the noise tremendously, but the whine is still there when the music is very low. I need this to be fixed because of the following reason which i will try to explain to the best of my ability. (I know nothing about installation...my friend is doing it all, which I will print this out and give it to him). The aux in for the headunit is actually a PAC adapter that allows me to run the audio from the PC through XM radio. This adapter switches modes automatically while in XM mode as soon as it recognizes sound from an external source...the PC. The problem lies in that since the whine or static occurs while the pc is playing, it will never allow me to listen to xm radio while the pc is playing....even if I mute the song in frodoplayer. Since the static is still there, XM chopps back and forth from the pc sound and actual xm radio. Can anyone please help me?? Thank you