Hi, i found this article by Ken Slovak on Outlook 2003. Maybe the part about "doesn`t play for all emails and approx. every 5 minutes applies to Outlook 2007". Attached-
I`ve also noticed that when i first turn Outlook 2007 on the email will come straight in and the sound will not play but if i send an email to myself and wait and leave Outlook open the sound will play. I solved this a fair while ago. Google for Ken Slovaks article. Cheers