How do I stop Excel showing (hide)

[Softparts]

I am using VSTO 2010 & Excel 2007 to generate a report and save it as a PDF with no user intervention. Problem is that Excel pops up when it executes the Open statement or if minimised shows on task bar.

The VSTO code:
Dim xlApp As New Excel.Application
xlApp.Visible = False
xlApp.DisplayAlerts = False
xlApp.UserControl = False
xlApp.ScreenUpdating = False
xlApp.WindowState = Excel.XlWindowState.xlMinimized
Dim xlBook As Excel.Workbook = xlApp.Workbooks.Open(sheetPath)

Everything I can find says visble=false should have fixed it. What do I need to do?

Daryl