that vent is a one-way valve for gases to escape the differential. when the differential is cold, the gas inside contracts creating a suction, when you take off the vent, you hear air rushing INTO the differential.
2012 V6 Base. 6-speed. 3.31. Roush Wheel Hop Kit. BMR 38mm Front Swaybar. Camber Modded Koni Yellow Struts. Linear Steeda Sport Springs. J&M Camber Plates. J&M Panhard Bar. Airaid Intake. 93R Bama Tune. BBK Ceramic Shorties. Carbon Fiber Trac-Lok w/ Finned Cover. Hawk SR pads. GT Rotors. Spec Al Flywheel & Stage I Clutch, 18x10.5 ET38 Enkei PF01 Wheels. 285 30 R18 RE-71r tires. Boss 302 Radiator.