Audio Systems: My car stereo is muted but amp is still working..., heavy duty battery, rca cables

Question
My subwoofer even when the sound is muted is still kicking. It's like if i was playing a song with a lot of bass. the cab lights fades everytime the sub kicks. I disconnected the rca cables from the amp and it stops. I have checked all the wires (all of a sudden this begun to happen). I don't know if the problem is the amplifier. I use a cap. When the sound is muted the cap shows 13.2V, 13.4V and when i disconnect the rca cables it goes back to 14.4V. I also replaced the rca cables with a new one but still the same problem. Ground and 12V wires are new and tick.  

Answer
What do you mean when the sound is muted?  When the mute button on the head unit is pushed?  If so, have you checked the mute feature setting?  Some units have choice if you want to mute all audio or just the main channels, but keep the sub output going.  Check your owners manual on that.

What happens when you disconnect the power cap?

What happens when the remote wire is disconnected from the sub amp?  Does the cap voltage go back to 14.4v?

If any lights dim when the sub amp is hitting hard it means you do not have enough battery power or the power cap is not sufficient or not connected in properly.

You should check the power cap ground and all connections.

You may need, independent of the mute problem, a heavy duty battery and alternator - if the amp really is drawing that much power off the system.  Power caps are nice for short term bass blast, but if you are playing music with solid bass repeating frequently the power cap soon becomes discharged and is no help in sustaining the voltages.

Let me know if there is more you need.