36 - iMac G5, 17-inch Troubleshooting Symptom Charts
Fan Sound

Loud fan noise coming from inside the computer

The grill on the bottom of the iMac G5 lets a trio of fans draw cool air into the system.
Advanced thermal software spins the fans fast or slow as needed, passing the heated air
through a slit on the back cover. As the system usage increases, the fans will adjust their
speed using advanced thermal software to meet the cooling needs of the system.
Accumulating dust can obstruct the flow of air through the system causing the fans to run
faster than normal. In severe cases the system may overheat and unexpectedly shut
down.
Under normal conditions, rotating fans will make a slight hum that varies in relationship
with their rotational speed and the amount of air that they are moving. In addition, the
normal functioning of the hard drive and optical drive will generate additional whirring and
scratching sounds that may be audible. All of these sounds are normal and do not indicate
a failure with your computer.
To begin troubleshooting a possible fan issue, we need to qualify the sound that you’re
experiencing.
1. Does the sound occur only under specific light/heavy usage conditions?
Yes: CPU intensive applications such as iTunes, Garage Band, DVD Player, etc., or
two or more applications open at once will cause the fans to run at an increased rate
making them more noticeable. If the sound only occurs when one or more of these
applications is running, this is normal.
No: If the sound isn’t affected by CPU intensive application it may be due to other
factors. Go on to the next step.
2. Is the sound always present, or does the sound vary?
The sound is always present: The normal functioning of the hard drive and optical
drive will generate additional whirring and scratching noises that may be audible.
Let’s see if this sound is related to one of the components. Go to step 4.
The sound varies: Under normal conditions rotating blowers will make a slight hum
that varies in relationship with their rotational speed and the amount of air that they
are moving. Let's see if this is indeed the case. Go to Next Step.
3. Are the fans making a normal humming sound that increases/decreases in relation to
processor usage? As the fans increase their speed to cool the system the sound level
will increase.
Launch the Activity Monitor application included with Mac OS X in the Utilities folder
to determine whether the noise corresponds with heavy usage of the CPU. Does fan
activity increase / decrease with the CPU Usage graph in Activity Monitor?
Yes: As the system CPU usage increases, the fans will adjust their speed using
advanced thermal software to meet the cooling needs of the system. As the fans