I have a very strange problem with my system. I have a Clarion CZ702 head unit and a US Acoustics 4050 4 channel amp. It's been working fine for about a month. I suddenly noticed the other day that I wasn't getting any rear sound. I checked the RCA's going into the amp, both front and rear channels, along with the speaker wires coming out of the amp. I unplugged the RCA cables and tried connecting the rear channel RCA's to the front inputs. When I did this, the front speakers came on. Very odd. So, I only get sound from the front speakers, regardless of which RCA's I plug into the amp. What could be wrong here? I'm very confused.