Radio and speaker problems on my 2002 Nissan Sentra GXE...Please help! :)

[nissansentra2002]

I have a 2002 nissan sentra gxe. This question is about my speakers (and possibly deck). I bought my car from a dealer in 2004, it had 22000km on it, so it wasn't new. It has 2 speakers in the back (20W) and 2 speakers in the front door panels, with 2 column tweeters. I was told that my system was supposedly a Rockford Fosgate, and it looks like online pictures of similar sentras with RF systems, but nowhere on my deck or anywhere in my vehicle does it say Rockford Fosgate on it. Additionally, I started to hear my back driver-side speaker start to crack, and then suddenly couple months later, the whole driver-side went very very low (almost no sound). I assumed that I had blown my speakers, so I purchased Alpine S-Types, two for the back, and 2 for the front with separate tweeters. My friend helped install them and splice the wiring to connect everything up. However, even with new speakers all around (except for the tweeters, which we were too scared to install the Alpine ones because we didn't know how to remove the stock ones) the sound coming out of the speakers is still weird. For example - with radio on, my driver side is quieter than my passenger side. Using an FM transmitter and my Ipod, the driver side is so quiet it might as well be considered no sound. BUT, oddly enough, when I'm using my CD player function, the driver side is crystal clear and good volume, and the passenger side is now the one that is dead sound (very very very low). I looked online, and someone else had similar symptoms and was told that it was an IC (IC? what is that?) problem. Can anyone help me with this? What need I do to get my car audio back on track? Where should I take it? Can I do it myself? Need I buy a new deck? Thanks....

[Faja]

It sounds (pardon the pun) like your headunit is the one at fault here. I'm guessing that the IC is "integrated circuit" which is a most likely one of the circuit boards in the radio itself. If you have another old radio you can test out the speakers and you'll know for sure.