Just a speculation, but have you considered an exhaust leak from the header or exhaust (cat)? Typically exhaust leaks are rpm dependent and can have a high pitch noise which get louder as a greater volume of exhaust travels through the system. Based on the service manual, nissan has metering equipment for diagnosing unknown sounds from the chassis and related.
It may well be electrically related, but worth considering any other variables regarding rpm dependent issues.
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