Have you ever tried to set up a program like HL2 on a comp with no Internet connection currently and the closest one is dial up?
Steam is a pain for dial up, wont bug me as much anymore, I have high speed now, woot. Yet steam locks out all dial up users.
Although I have heard those turret sound effects before, I have also seen turrets that shoot and look nearly exactly like that, from a game also made by valve.... hmm HL2...