1996 Jeep Grand Cherokee

Electrical problem
1996 Jeep Grand Cherokee V8 All Wheel Drive Automatic 189000 miles

My rear left speaker makes loud scratchy noises sometimes. The speaker is fine because when I put another one in it's place it does the same thing. Any suggestions? I assume the only other thing it could be is either the wires coming from the speaker going to the back of the receiver or the reveiver itself. Any ideas on how to troubleshoot this problem. I do have a multimeter if I need one. Thanks.
October 10, 2010.

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