Diesel subs don’t operate their engines while submerged unless they are recharging in safe waters, so there aren’t any ‘explosion noises’. They have batteries

Diesel subs don’t operate their engines while submerged unless they are recharging in safe waters, so there aren’t any ‘explosion noises’. They have batteries that are used for propulsion, and the Diesel engines are technically generators, as their propulsion system is electric - like a train.