I usually see these alerts in APM Alert for Hardware Sensor Alerts. There are two pre-canned alerts that come out of the box. If you check the Advanced Alert Manager you should see this alert as Application Hardware Sensor Critical and there is another for Warning. If these alerts have been deleted then you would have to check if any of you alerts have APM.HardwareSensor as a value to trigger on.
Hope that helps. If you could provide screen shots I may be able to identify for sure.