Speaker troubles

[Sloth_n@med_Speed]

I installed an android headunit a while back, which worked fine until a few months ago, when the speakers would randomly drop out. Sometimes all at once, sometimes a few, or even one. Sometimes they chase each other round the car... so super annoying.
I have since installed an alpine booster pack, with and rca input, and also re-wired the speaker wires to the booster pack, so I know the problem isn't with the stereo or Holden harnesses. Any ideas as to what the problem is?

 

[Fu Manchu]

Connections to the speakers themselves loose?

 

[Sloth_n@med_Speed]

Connections to the speakers themselves loose?

Have been avoiding opening up the doors to have a look, but would seem thats the next step.
It just a bit weird that they started dropping out at the sametime.

 

[Sloth_n@med_Speed]

UPDATE: so spent the last few hours going through the system and cleaning up any potential grounds. Seems to have done the trick, but the front passenger side speaker is quite dull, and whines with acceleration. So it looks like the next step is to re-wire the speakers.

 

[Fu Manchu]

If it is whining then I’d be looking at the headunit.