Just my opinion, but I think DW uses a basic sound profile for most of the subs. Meaning, the sound profile doesn't change based on speed. There are some exceptions- ie, the Jin and Xia class are "randomly noisy" on purpose and you'll get a "clank" out of them at times. For the rest, each class gets a background sound value. So, its not like the reactor coolant pumps shift to a higher power level above X knots and produce more noise. Also keep in mind that your engine room is ALWAYS producing sound. Even at All Stop the generators are still producing electricity.
In vanilla DW (and the LWAMI mod) and the older versions of the game, depth tended to hide noise. Higher water pressure meant you could drive the boat faster without creating a lot of sound. This has changed in the RA mod (again, IMO and plaese don't shoot the messenger) and its why I've written in the past that there's no where to hide in RA.
Always check your XBT display at the start of a game.
This is the last screen option in Sonar. You want to know what the conditions are underwater and if you have a sound layer to work with. Our Resident Chazly
has done some great vids on YouTube that explain sound layers and sound channels in DW.
You can also get a good idea of surface conditions by driving up to PD at some point and looking for differences on your broadband displays. Higher sea state means more background noise, which is good for staying undetected but bad for tracking contacts. Bottom type can also be important if you can get close to it. A rocky bottom can be thought of as neutral while sandy or muddy bottoms tend to block or muffle sound.
As you gain experience in DW this gets easier to figure out but you could also open the mission in the Mission Editor and check the environmental conditions.
