Back speakers don't work all the time

I have a 2000 GPGT and the speakers stopped working about 3 weeks ago. I'm not sure if it's the weather or not but I seem to think it may be the warmer weather that allows the back speakers to work sometimes. I got in the trunk and wiggled all the wires and that did nothing to help. I was wondering if anyone had any ideas on how to fix it. Thanks

The upgraded stock stereo in my 98 has a stock amplifier directly behind the glove box on the passenger side. I would check those wires. Also, i had a leak one time in my a/c intake and this caused some water to drip onto the amp causing the back speakers to have static. Hope this helps.