It could be a fan issue, an issue with the fan controller on the board, an issue with the temperature sensors, or even a strange issue with software. On the software side, I have only ever seen that with video cards that let you control the fan speed from the driver.
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Try something like OpenHardwareMonitor and check that the temps are not jumping around when they should be hot-running. This can help you detect a faulty sensor. You can also get the RPM of the fans from OHM.
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EDIT: Removing OpenHardwareMonitor suggestion. Saw in second video you have a monitor going.
It could be a fan issue, an issue with the fan controller on the board, an issue with the temperature sensors, or even a strange issue with software. On the software side, I have only ever seen that with video cards that let you control the fan speed from the driver.
Try something like OpenHardwareMonitor and check that the temps are not jumping around when they should be hot-running. This can help you detect a faulty sensor. You can also get the RPM of the fans from OHM.