use the KeyPress Event to stop the Beep ( e.Handled = true for the Enter Key ) eg:
PHP Code:
        private void textBox1_KeyPress(object senderSystem.Windows.Forms.KeyPressEventArgs e)
        {
            if(
e.KeyChar == (char)Keys.Enter)
            {
                
// stop the Beep like this...
                
e.Handled true;
            }
        }