Worksheet Change: Formula in Target Range

The target range in my worksheet_change macro is comprised of formulas. The event will not run because the target range is formulas. Is there a way to re-write my macro so that the worksheet_change can recognize a formula?

Private Sub Worksheet_Change(ByVal Target As Range)

If Not Intersect(Target, Range("aa4:aa53")) Is Nothing Then
If UCase(Target.Value) = "TRUE" Then PlaySoundFile "C:\Windows\Media\Notify.wav"

End If

End Sub