I think it is much more likely it is the speaker than the wiring...You probably have an intermittant voice coil in that speaker...To test ....While the radio is playing put your finger on the cone of the speaker and push it in and see if the speaker does anything weird...If so it is the speaker....my 2 cents

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83 300CDTurbo 307,000
2005 Honda Element 266,000
56 Nash Ambassador Country Club Special 34,000(under restoration presently)

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