Axxcess Ipod cable installed, speaker trouble

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Hello folks, so i just installed the axxcess ipod cable into my single disk non jbl head unit. However when i plug in my ipod to the adapter, I'm getting a lower volume output from both rear and front left speakers. THe right (rear and front) speakers are just fine with good base and treble. I've checked the fader and balance and they are both aligned. Is there anything else I can check for before returning this thing? Thanks!