The damage of this mid-power MOSFET surprises me. Audio circuit is probably consumes just a few tens or hundreds milliamps at most. Yet it has a drastic crater

The damage of this mid-power MOSFET surprises me. Audio circuit is probably consumes just a few tens or hundreds milliamps at most. Yet it has a drastic crater-like dent in the IC enclosure. That tells me it was a voltage surge or current spike. The hypothesis of entering a linear region caused by a random software glitch producing an unconscious PWM on a filter slope sounds plausible as well. But that crater-like dent says that the real cause might be way more intensive than that.