Intermittent Front Speakers
I tried a lot of the suggestions, many of them detailed. Too detailed. The easiest and simplest was taking off the door panel, pulling the speaker, and putting a meter on the wires attached to the speaker (with the key on to provide power). It indicated power, so I replaced the speakers.
If you don't have a meter, you could see about checking with another speaker that you know works. KISS. Of course, there will be others with more complicated issues that need to be resolved.
Basic speakers in a G6 aren't worth squat. I have spoken to many current and former G6 owners and the consensus is that the base level speakers on a G6 aren't worth squat.