FotRSU does not allow Mk14s on an Sboat, and it does not allow Mk10s on any from V-class up through all the Fleet Boats. It's not in the equipment files. If you are getting that, then there is a cross-contamination of your mod and / or Save files Michael Wood. That was done by CapnScurvy to prevent what you describe. It'd be best to de-activate the mod, and try again. You will most likely have to do a new SH4 install, and empty your Save folder in "My Documents", then try the mod again. If you want to run multiple mods and / or stock on the same computer, you could familiarize yourself with MultiSH4, and use that to segregate your Save folders.
@ merc4ulfate: Be sure you work on a copy of the file(s), and build yourself a mini-mod, but if you have S3Ditor, you can use it to open the Data/ Sounds / SH.SDL file. Use the Edit menu, Find, and search on "crash", and it'll take you right to the Submarine.IntCrashDive segment. In the right-hand portion of the window is a Volume: editable box and slider, which is sitting at 97. Try something like 50-60 initially, which will probably be too quiet. Notice toward the top of that section that there is a little "Play" button, so you can use that for your comparisons while in S3D. All I can find for the sonar station (besides the pings) is Ambient.Hydrophone, and that's just the background noise of the ocean, not the sound of the ships. I did find several, such as Ship.NCL_Dido.Propeller, and those might be the files to hear the props - but I do not know for certain on that...