air conditioning - hissing sound when car is turned off for about 10 seconds on 2004 Ford Explorer

ac was not too cold, hooked up the recharge unit and adjusted for outside temp 85 degrees, said pressure should be between 45-55psi, emptied can and pressure was about 45psi. ran car for a few miles, seems like temps are colder but when I turned off the car I hear a hissing sound for about 10 seconds coming from the area near the ac lines. but I can't see any oil or liquid on any of the lines. tried it a few times, same result. turned off ac and then started and turned of car, no hissing sound.
did I over charge? or is this normal. Can only hear it when the hood is up and you have your head over the engine.

Asked by for the 2004 Ford Explorer
Pressure equalization, normal operation. No worries! They all do this.
Thanks for the quick reply!
No prob.