Audio Systems: Speaker/amp issue

Question
I have a 2009 GMC Acadia with the 10 speaker Bose stereo system. When I first bought the car I noticed the driver side rear door speaker would cut in and out.  If I turned the volume up, the speaker would come back on. This would not last however as it would cut out again and I would have to turn the volume up and so forth.   I replaced the factory head unit with a JVC unit and the four door speakers with JBL component speakers.  This did not fix the problem as it still does the same thing.  The installer checked the wiring and said it was okay.  Could this be a problem with the factory Bose amplifier? Should I replace the amplifier and hope this fixes the problem?

Answer
My first guess would be a wiring problem. The condition you describe is very much like a broken wire inside the speaker voice coil assembly.  But, since you have replaced the speaker I think you should check the wiring to the speaker cutting in and out.  Move, resolder, check connectors, etc.  And, yes it could be the amp or even a bad connection at the input of the amp.

Intermittent conditions are hard to find.

PS: If you are handy, you could run an open wire from the output of the amp to the speaker that is cutting in and out. This wire would be in parallel with the one already in the car.  It would tell you if the intermittent is bad wiring or the amp.