There's an achievement for getting the armoured car to drop without shooting at it in the Slaughterhouse mission. Like the achievement says, but how?
It seems like you just have to survive three waves when the van is hanging, without shooting the wires that hold it up. The van will drop without you having to do anything.
This video might also be helpful:
First of all, you'll have to shoot at the convoy (the red van) windows. This will make it fall differently, trapped in cables with the trunk facing the sky.
Once you reach the slaughterhouse, instead of shooting at the cables to make it fall, wait for three assaults (you might prefer to achieve this in normal difficulty, now that it's possible, thanks to the last update ;)). Then the van will fall down by itself and you'll get the success.
Note that with this method (shooting the van at the beginning), there's no extra money drop with the safe (while you'll find some cash if you let the van fall trunk first and open it with C4).
Good luck !