Raise the volume in the game:
Then raise the volume in your pc or headphones
Turn off engine to make the hydrophone all quiet
Try this for the first time in training mission "Convoy attack". If you can't hear the noise even after this it means your installation is not working.
And make sure you don't use a mod that lessens traffic in the sea. Mediterranean mods or Black sea mods might take out traffic in other sea areas to make the game load faster.