[herefordman]

I'm with 2000CAYukon on this one, the rushing noise is almost certainly the coolant not the transmission.
Look closely to see if the heater core is leaking even a small amount, this will cause it to aspirate air when its parked rather than leak fluid.
Sometimes the tanks on either end of the heater core need to be crimped, the crimping done during assembly sometimes works loose. The plastic panel below the heater core comes off, and the core is very easy to see and get at. Watch out the panel may be full of leaked coolant.