No words of wisdom yet, but I'll check the wiring schematic for the rears. First place to check are those left and right wire harnesses at the trunk hing points. Verify as best you can that nothing looks pinched or crushed.
Can not speak about the 2008 but on my 2002 the speaker wire runs up the inside trunk by the hinge and I had a wire get cut by the hinge. Spliced it back together and put some tape on it moved it away from the hinge best I could. Works fine now.