fyi.... I experienced a similar problem of the Windows "Default Beep" frequently sounding when I switched between different Excel worksheets from the taskbar in Windows 7. Traced it to the installation of a MySQL add-in, specifically "MySQL.ForExcel", which on my computer resided at this address: C:\Program Files (x86)\MySQL\MySQL For Excel 1.1.1\MySQL.ForExcel.vsto|vstolocal. In Excel Options, Add-Ins, I selected Manage "Com Add-Ins", clicked "Go", de-selected "MySQL.ForExcel", said "OK", and immediately the beep sound was gone.