Every 1,609 days, the iPhone SE is designed to revert to an old TV tuner.
But since it expects analog signals, it produces static instead.
It's a feature!
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Sorry, have no idea what happened (obviously!). Although, truth be told, sometimes audio oddities can happen due to insertion of headphone jack, which might not make proper contact. I've had sound vanish on old I-devices. A restart usually clears that up.
Had you used the headphone jack recently?