I know you can get MWP to Notifiy you when there is an error but this uses the default Windows sound from C:\Windows\Media\Windows Background.wav and so as there are a number of other apps that use this sound, it's difficult to know that MWP has raised it as there is no visual notification at the time. I would therefore like to suggest that a custom sound can be used for this, just like you do for New Mail. It might aslo be worth having a Notification pop up too.
Note that I only found that it was MWP making a random 'boing' by using Systernals 'Procmon' to trace what app was calling the sound (.wav) and it turned out to be taskhostw.exe that played the sound after a 'FAST IO DISALLOWED' event was generated. That event was generated as MWP was trying to access a mailbox (Hotmail as it happens) that had had a password change and as Hotmail uses POP for 'applications' to access it, MWP could not access the resouce it needed, hence the error. Had MWP popped up a dialog or played a different sound, i would have saved serveral hours pinning this one down
Cheers
Paul