The tank killed me the first time and I was surprised by it as I didnt even see it at first. So after I restarted I looked at the ground and saw the tank tracks and was able to figure out it comes from the door to the right of the bunker you emerge from. It's actually coming out of the area where you first hear mention of the general leaving. You go through that area earlier in teh mission. Easy kill though with mines and really easy if you toss them from above by climbing the ladder.
I just wish the Top of the Heap wasn't a 16 player achievement. Who thought 16 players would ever play the multiplayer at once?
-Insert something creative here-
( that doesn't include stats that no one really cares about or some poorly photoshop'd image with your name stuck in it. )