Surface noise? What, the bubbleheads don't know how to use sonar anymore? Or look up?
Nah, the USN released a comment that the ships were conducting security operations of some vague sort at the time. Considering how loudly Iran has been talking about sinking infidel warships...I'm still betting the sub was intentionally hiding under the ship, using the sonar return from the ship to make the sub invisible, when someone cut things too close.
USAF uses the same tactic (blending two signatures) to move spy planes in "under" commercial aircraft. That's generally considered part of the reaosn why the Soviets shot down KAL007 some years ago, they knew that recon aircraft were playing similar games to enter their airspace.
Exactly what happened is operational intelligence and will never (ok, maybe in 30 years) be disclosed to the public. Even if the possibilities are limited and publicly known. And that's as it should be.
Gonna be another vacancy at the command level unless there was a major systems failure, though.