Heavy click noise under acceleration

[buexdreux]

I have a heavy clicking coming from the rear when I accelerate to >110 mph and when decelerating to around 110 mph. Not sure if this is coming from the differential or not, but i'm assuming it is. Whenever this does happen I'll check under the car and notice a small amount of diff fluid coming from the vent tube. The heavy clicking only happens when the car is at that speed and the diff fluid only comes out of the vent after the heavy clicking. Could this be caused by overheating of the diff fluid? What else could this be? I'm investing in a diff cooler from FTBR because I'm planning on getting into auto cross and I was hoping this would fix the issue. Thanks for all input