Tac31, when you crash on my mission, do you by any chance leave your group and charge straight up the hill, and have it lock up in the dead space just below one of the dshks?
By the way, when it crashes, the audio crashes too. The weird sound you're hearing is the audio equivalent of the screen freezing.
I have Win XP Pro/1.44 TBird/Radeon 64 DDR/SB Audigy and get lockups. When building my mission, I couldn't test it allt he way through because of crashes. Now I hardly get them. (=I finish the mission several times over).
And when it crashes, hit ctrl-alt-delete, then Alt-E, then Alt-E again (and maybe a few more times just for good measure). In a few minutes, the desktop will come up.
Or that's what should happen.