Noise issues tend to be hard to nail down. Make sure you have not created the problem by first disconnecting all of the externally connected devices. Also make sure your AC outlet is properly grounded and you are using either a good surge suppressor or a UPS. Sometimes noise can enter your system from a connected device or power line that is not properly grounded. If after that you still have an issue its within your system.
Lucky you gave us a good clue here, the load of the CPU has a correlation. To be doubly sure I would recommend you run both Activity Monitor (in your utility folder) and TG Pro to make sure you aren't hitting a heat issue.
As long as you're not overheating the issue is likely within the main logic board one of the noise caps. The tricky part here is isolating which one is failing. If you can I would visit an Apple Store to see if this is covered under an extended warranty as it could be a defective part. Otherwise you are either looking at replacing the logic board or finding someone with the needed skills and tools to isolate which cap needs replacing.
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