Okay, in the Dashboard.log file, I found an entry that tells when the event was fired:
[7188] 130703.200145.3240: AlertsViewer: UpdateItem COSMOS 7/1/2013 7:29 PM,Free space is low on hard drives
Now for the trick question, why? I'm not seeing anything in the logs (and there are a log of them) around that time that look related...
@drashna, I would be glad to upload to Dropbox. In the meantime, I'm going to email Covecube support.