William stops dead in his tracks and hears the noise no marine ever wants to hear in an infestation zone.
Beep.
Beep.
Beep.
He raises his rifle and stares in the direction the noise is coming from.
Beep. Beep.
Then suddenly, a crash as an air vent falls about 5 meters in front of him. Then, an angry xenomorph with it, it charges directly towards him. He pulls the trigger, firing a flurry of pulse rounds at it, riddling it with holes and making it drop dead.
The beeping stopped.
"Take that, son of a bitch.", kicking the corpse in disgust.