Why the Power Macintosh G4 MDD (with noise reduction kit) is louder after waking from sleep

We previously reported on complaints about Apple's newly shipping Power Macintosh G4 MDD noise reduction kits (which include a replacement power supply). We noted that while the majority of readers have reported success, others note gradually increasing noise levels when waking from sleep after installing the kit.

MacFixIt reader Ken Marks has a logical suggestion for the added loudness - which can also be observed on systems without the new kit:

"When the computer goes into sleep mode, there is a heat buildup inside the computer due to the fact that the fan stops. The sensor reads this and tells the fan, upon awakening, to increase its speed. If left asleep long enough, the heat seems to dissipate and the fan does not increase its speed upon awakening. Also, if left asleep for only a brief period of time, the sensor has not had enough time to read any increase in temperature, therefore the fan will not increase in speed."

This makes sense, as machines generally take 5-10 minutes to resume normal noise level depending on the ambient room temperature.

On a related note, some users are reporting an 8dB reduction system sound level at maximum fan speed.

Feedback on this issue? Drop us a line at late-breakers@macfixit.com.

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