FREQOUT makes sine waves and must be filtered, which is not what you need.
Try this ...

Code:
PiezoPIN  VAR PORTC.2
TMR0IF    VAR INTCON.2
Width     VAR BYTE
OPTION_REG = %11010011 ; TMR0 1:16

Alarm:
    FOR Width = 161 TO 120 STEP -1
        WHILE !TMR0IF
            TOGGLE PiezoPIN
            PAUSEUS Width
            TOGGLE PiezoPIN
            PAUSEUS Width
        WEND
        TMR0IF = 0
    NEXT Width
GOTO Alarm