I have a all stoc 99 alero gls sedan and only the rear speakers are out. My whole audio system is stock. Is this a head unit problem or could both rear speakers have blown same time mysteriously? I did have a system (2 12" subs and 600 watt amp) that I ran the rf converter behond the radio for signal to the rear speaker wires on the harness, could I have blown the speakers doing this or fried my actual radio itself? How would I go about getting this tested if it could be eitherof the 2 Id rather not replace both rear speakers AND the whole radio itself