Depends if the cooling fan or the condesor fan is coming on. If it's the condensor fan coming on it would be becayse the a/c compressor is engaging. If its the cooling fan, then it's because the coolant temp sensor is not working properly and the ECM believes the engine temperature is higher than it really is or that the sensor is failed and as a fail safe mechanism it will run the fan all the time.
Intermittent squealing while driving can be from a few different things. does it sound like belt squeal?