Some of the FrightProps wireless triggers beep when activated.  To disable this feature you must remove the beeper from the base station.

The picture shows the general location of the beeper.  It might have the white label on it as shown in the picture, if so remove it. The beeper looks like a small black cylinder with a hole in the center. 

If you have a soldering iron the best way to remove it is to de-solder it from the circuit board.

If you do not have a soldering iron you can gently rock the beeper back and forth until it snaps off.  It might take 50 or more rocking motions.