I assure you that the background sound is mostly annoying, not fun
. But as I've already said, that was it's main idea. To keep you, the captain, away from checking up on the ear-bleeding sonar man. Since the RFB sounds are very close to reality, they are a pleasure to have by themselves. I have no idea if the engine sounds were that potent around the sub, and in what measure they affected the hydrophone. The game only makes the original sound (the slow speed i think) faster, higher in pitch and louder as the engine revs up. I can't control by how much, so I could only get a loud noise at high speed by starting from a moderately high volume (that you can hear as soon as you leave the "all stop" setting). But any audio application can alter the volume of a wav file, so it shouldn't be a problem to adapt it to your needs. The new sound saved me once from a quick death, as the nav officer went to standard speed while I was approaching a convoy and had to input a new course.
Dodging depth charges also seems more... envolving... as you lose contact with your enemy when going to flank speed.