Do you have any idea why the fan would be surging? The computer isn't overused, and the only thing I currently have open is Firefox. This is perplexing to say the least.
If there is poor contact between the HSF and CPU, the CPU will almost instantaneously heat up even under mild load and the fan controller will respond by increasing the fan speed. Once it goes back to idle, it almost instantaneously cools down and the fan controller slows the fan down. Rinse and repeat.
When the HSF is making good contact with the CPU, the warm up has a much gentler slope, the fan speed ramps much more slowly and the resulting noise is far less annoying.