It's definetely the speaker. It's even there when you fade out the back speakers. The only way to get rid of it is to turn off the radio or disconnect the speaker.

I have an '05 M&T Vibe. The left rear door speaker clicks and, recently, has started crackling as well. The dealership appears clueless as to what is wrong. They've replaced the CD player twice, the speaker twice, the amplifier, and this week, the ground wire. STILL the clicking! Part of the pro...