Are you sure the icon is not hide by XP at system tray? You can configure XP for hide some or all icons in system tray…
If I understand you, you have the ‘a’ blue icon (merged or not with the ‘i’ icon) and only from time to time the second (or third) icon of ‘email scanning’?
Into avast settings you can configure the last icon as you may know…
All icons and its configurations could be set directly into avast4.ini file. More information about the avast4.ini file you can see here.