If you are using the ITC-308-WIFI, please refer to this post:
Please check AH (High tempearture value) and AL (Low temperature value), they are related to the alarm sound and their settings are separate from the temperature control settings.
Depending on your settings, the ITC-308-WIFI will control the heater and cooler to maintain a temperature range of 4C-11C and if the temperature reaches or falls below 3C it will trigger AL alarm. However, because temperatures may fluctuate, 3C is close to 4C. If you do not need the alarm function, please set AL to 0 so that it will not trigger.