Interface alerting on speed changes

I am working on a way to auto acknowledge the event "Interface speed changed from ******* to ******* ".   I am aware that I could disable the entire event type with

UPDATE EventTypes
SET Record = 0
WHERE Name = 'Interface Changed'

but that seems like overkill.  I think they way to approch this is to just have the system clear the event.  The only way that I can come up with a way to do this automatically is to use an alert.  I have tried creating an advanced alert with the trigger being as such

Trigger Alert when all of the following apply
     Interface Speed has changed

I have no reset condition or Alert suppression
I have the Trigger action of writing to a log file with the following statement

${AlertTriggerTime},${NodeID},${NetObjectID}

If I test the Alert it does write out the log file as expected.
The issue seems to be that I can not get the alert to trigger on its own.  I will get the events of the interface speed change but it does not seem to trip the alert.  Any ideas?