Extra noises of the all the search and rescue assets in the vicinity and the natural biases of the human operators to want to decipher patterns from the background noises = false positives. There’s precedent for that:

https://www.forces.net/usa/banging-sounds-heard-during-search-sunken-us-submarine-uss-thresher

This is actually quite normal, and similar situations have occurred during search and rescues for missing submarines. The ocean carries sound quite well, and hydrophones will inevitably pick up noises of from all sorts of of things if observed for long enough. Add into that the extra noises of the all the search and rescue assets in the vicinity and the natural biases of the human operators to want to decipher patterns from the background noise; false positives are quite typical.

A similar situation happened with the sinking of the USS Thresher. https://www.forces.net/usa/banging-sounds-heard-during-search-sunken-us-submarine-uss-thresher