All the previous suggestions are good ideas and definitely worth checking, but according to the book, for hot weather it is normal. Read below. This is a direct quote from the owner's manual.
Your vehicle is equipped with an engine driven cooling fan drive (also
called a fan clutch). This fan drive changes the fan speed to match the
vehicle’s changing cooling air flow requirements. Fan speed, fan noise
level and fuel consumption all will increase based on the driving
conditions that include trailer towing, hill climbing, heavy loads, high
speed and high ambient temperature, individually or in combination. The
fan drive is designed to provide the minimum fan speed (and resulting
fan noise and fuel consumption) required to meet the ever changing
vehicle cooling air flow requirements. You will hear the amount of fan
noise increasing and decreasing as the engine power requirements and
vehicle driving conditions change as you drive. This is to be expected as
being normal to the operation of your vehicle. High levels of fan noise
might also be heard when your engine is first started, and should
normally decrease after driving for a short time.
Now if the fan spools up and stays up, then you might have a problem with the fan clutch. But it sounds like that isn't your problem. Since yours is coming on at odd times, it might very well be a coolant level issue. Mine cycles too, but only when it's really hot outside (mid to upper 90's) and only when I've been idling for a couple of minutes at a stop light or in stop and go rush hour traffic. It always goes away after a few seconds.
Last edited by cp2146; 07-03-2012 at 06:16 AM.