12w3v2 Started making distorted bass noise at low...

Connect each speaker coil one at a time to a square 9 volt battery and watch for the cone to move.

Also try hooking another speaker to your amp just to make sure the noise isn't in the amp.

You can use a 9 volt battery to test wire polarity also. Hook up the + wire of the speaker to the + terminal of the battery and the - speaker to the - battery terminal. If the speaker moved UP or OUT then the wiring is correct. If it moved IN or DOWN then the + and - wires are backwards on the speaker.

Also if you have two or more speakers hooked together test all the same way while they are hooked to each other. ALL of the speakers need to move in the same direction at the same time.

Clipping causes more speaker damage than anything. "Dirty Power" can happen in good quality amps too. The gain control is to match the voltage between the headunit and the amp. It is NOT a volume or boost knob. If you overdrive the first stage of the amp and then clip it damage will occur to the amp and speakers at some point.

Hope this helps.