Most likely the mission was not written for RA 1.40. You can open it with editor and check the triggers, name of units ecc ecc ecc
About sound of stream and retreiving...You right, it's too loud. I change station when I streaming or retreiving the towed array. I dont know if it's possible to change that sound and not others.
About your others questions, FPSChazly and P7P8 have already answered.
