Cracked Pressure Hull Hint

USS Toledo's (SSN-769) unexpected pressure hull fault is one thing - small. The outer hull crack was somewhat longer. Strange that no one heard an usual noise like the splintering of steel. If the associated metal failure noise was not heard, where is the most likely place for it to have occurred?

HINT: Not out at sea. Not while the below decks was on watch (in port), either.

Is the sound of a dense metal suddenly cracking audible? Yes.

Is the sound of a dense metal slowly splitting audible? We must ask how slowly, then ask who would actually know something that esoteric. Answer: more people than you might think.

Something less unexpected is that when significant boat traffic is around killer whales alter their communication frequency. Why does that not surprise us? Do people not alter communication amplitudes in crowds and noisey locations? Last year, scientists discovered that killer whales emanate sounds up to 40 kilohertz, well beyond the range of human ear detection.

Reminder:
The (officially unlocated) Underwater Locator Beacon (ULB) for Air France's Flight 447 are a very similar frequency (37.5 Khz signal).
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Submarines are silent and strange.