Noise happened again .. .this time drove it straight to the dealer service department. Both the service writer and technician heard the noise and were able to see when it occurred. They found two stored trouble codes for the AMP that had occurred earlier not during this episode. I also explained to the technician that sometime the radio "pops" which he said sounds like an AMP problem. At this point they don't want to replace the AMP as they feel it could be something else, not sure about that. Waiting to hear back from them.