sounds like the park switch actuating. Theres a little solenoid type thinger in your shifter that goes off when you hit the brake so you can't put the thing in park if you don't have your foot on the brake.

Mine does the same thing. On my trooper, I got so sick of it, I used some electrical cleaning spray on the solenoid thing and it make the sound not so loud, but never got rid of it completely.