Well, I'm no expert and not an authority of any sort on the mysteries of SHIII...but...what THEBERBSTER pointed to should help you out.
Before I increased my machine's RAM and upgraded SH3.exe with the 4gb patch (or LAA), I had experienced saved games crashing when I was within 50km of anything when I saved and exited the game. Saving within 50km of land, ships, planes...anything including ships that I'd just recently sunk...seemed to be "poison".
Since you pointed out that the sound.act file seems to be the culprit, I'm wondering of you were inside that 50km zone from a ship, or ships, that you had recently sunk, but were still in existence below the "sea surface" slowly sinking and generating the sinking noises (even if you aren't within "hearing" range) that continue until the wreck gets to the bottom and "dissolves". Or, perhaps you were within 50km of another noise generating ship, including those in harbor.
Those problems that I experienced almost all seemed to go away when I applied the 4gb patch, but I still pay heed to that 50km "rule".
Good luck...good hunting...sink 'em all!
