Torpedo makes a bang noise just after exiting the tube on the surface

[Paul Riley]

I forgot to mention this before,during my earlier engagement with a ship on the surface at night,I noticed the torpedo made a sort of bang noise just after exiting the tube,almost like a small impact explosion.It also happened with my second attack from tube 2 later on in the attack.I quickly checked the front of the UBoat as I thought it had prematurely exploded just after exiting and damaged the UBoat in some way.
It seemed the torpedoes were fine and carried on to their target as normal.
My only guess is that the UBoat was high on the waves at the time of launch causing the torpedo to crash down heavy on the surface before finding its depth setting.Waves were 7mps by the way,not exactly the worst seas to be in for bouncing torpedoes,if this is what they were.

Thanks for any info on this.