iMac G5 (20-inch iSight) Troubleshooting — Symptom Charts 163
Fan Sound

Loud fan noise coming from inside the computer

The iMac G5 (20-inch iSight) has a trio of fans that circulate air throughout the system. It also
includes temperature sensors, and advanced thermal software that spins the fans fast or slow as
needed. As the system usage increases, the fans will adjust their speed using advanced thermal
software to meet the cooling needs of the system.
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.
Does the sound occur only under specic light/heavy usage conditions? 1.
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 aected by CPU intensive application it may be due to other factors. Go
on to the next step.
Is the sound always present, or does the sound vary? 2.
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. Check whether 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.
Are the fans making a normal humming sound that increases/decreases in relation to 3.
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? Check by running CPU
intensive applications such as iTunes.
Yes: This is normal operation and none of the fans require replacement.