Slowdown of a component (especially CPU or GPU). Thermal throttling means, the component slows down in order to prevent from overheating. This is a feature that is present in almost all newer processors.
Throttling does have no sound. But since the component is very hot at this time, you'll hear the fans rotating at maximum speed.
i7 in a laptop tends to run hot, so the occurence of thermal throttling wouldn't surprise me.