"i read a lot on uboat books and watch films. " Definitely first-hand experience there.
First time I ever heard Nautilus described as a 'modern' sub. Maybe in 1951...
Just to set the record straight. Nautilus was essentially a WW2 design with a nuclear power plant. There was absolutely no silencing technology applied -- no anechoic coatings, no rubber-mounted 'floating' platforms, etc.
The original issue was, can one hear 'burbling' sounds when underwater? My experience is, definitely not. Maybe someone who has stuck his head underwater in the pool would think being in a submarine would sound the same. Not so. Traveling submerged, the only way one would know that the boat was underwater is the absence of surface wave action.
Ditch the burbling sounds, if you want realism. That's my last word on the matter.
