L'alerte sonore ne se déclenche pas toute seule

Option Explicit
Dim MemoCell As String
Private Declare Function Beep Lib "Kernel32" (ByVal Fq As Long, ByVal Tm As Long) As Long

Sub BeepBeep()
Beep 392, 200
Beep 494, 100
Beep 588, 200
Beep 740, 100
Beep 880, 400
Beep 740, 100
Beep 880, 900
End Sub

Private Sub Worksheet_Calculate()
On Error Resume Next
    If Cells(2, 1) <> MemoCell Then
        Cells(2, 4) = 1 = " & Cells(2, 1).Value"
        MemoCell = Cells(2, 1)
        Call toto
    End If
End Sub

Private Sub Worksheet_SelectionChange(ByVal Target As Range)
    If Target.Address = "$A$2" And Cells(2, 1) <> MemoCell Then
        Cells(2, 4) = 1 = " & Cells(2, 1).Value"
        MemoCell = Cells(2, 1)
        Call toto
    End If
End Sub

Sub toto()
If Range("a2") = 1 Then
Call BeepBeep
MsgBox "Attention ALERTE!!!"
End If
End Sub