Troubleshooting the Power Mac G5 (#5): Noise issues; Optical audio-out and short sounds

Noise issues In our continuing coverage of the Power Mac G5 noise issue, it appears that Apple technical support is recommending a PMU (power management unit) reset to some customers who are having fan irregularity problems. We've also managed to scrounge up a few unorthodox workarounds, including placing a thick pad of paper underneath the G5 to prevent vibration:

MacFixIt reader Paul Burton is one of the handful of G5 owners who experienced a problem where the system goes to sleep, the fans rev to full speed, and the G5 cannot be woken.

"I spoke with a technician from Apple and described the problem in detail ? Of course, it was the first time he had heard of such an issue with a G5.  That said he suggested resetting the PMU pressing a button on the logic board inside the tower:

• Open the computer and remove the clear dust cover.
• Without removing the fan (in order to locate the button) - look down toward the lower left hand corner of the unit at the logic board (memory).
• Now, follow the lower edge of the logic board over to the right until you see left bottom rear edge of the fan unit.
• On the logic board, near this spot, you will see a small chrome square with a very small round flat-topped button in the middle.
• Press and hold this button for three seconds.

Burton says that since doing this approximately three weeks ago, he has not had another occurrence of the fan revving/sleep problem.

Do not get trigger-happy though - pressing the CUDA or PMU switch repeatedly can result in damage to the PRAM battery, causing its capacity to shrink from years to days or less.

Meanwhile, Stan Goldberg found that putting a thick pad of paper under his G5 - which started making excessive noise after a few days of quiet operation - helped to dampen the vibration of the G5's case against his desk, eliminating one source of unwanted noise:

"When I first got my dual G5 about two weeks after they came out the unit was quiet as can be. I was amazed how silent it was. Then after the loud rev up upon sleep occurred after about five days the front fan seems to have come on and makes a consistent humming fan noise and won't turn off. There is also high pitch sounds that come and go and seem to be due to vibration. Putting thick paper pads under the lower supports helped with the vibration transmission to my wooden desk."

Optical audio-out and short sounds When using the digital-out port option in the Sound preference panel on a Power Mac G5, the output volume is dimmed and (it seems) audio volume can only be adjusted via the external system's controls and/or a program's volume slider (as in iTunes).

MacFixIt reader Hans Havermann has some interesting observations about he limitations this can impose:

"Surprisingly, using the built-in audio option still channels the sound to the external speakers, but computer volume-control is not shown as disabled. However, changing the volume this way generally has no effect on actual volume. My real issue with all this is that the actual sound output in one of my favorite programs (ChessWorks) appears compromised (in either audio-out setting, using optical audio-out cable). Short sound effects are not heard (longer ones seem to be ok). My fix for this has been to have iTunes music playing in the background at all times, which appears to allow the shorter sounds to be heard as well... as long as iTunes isn't between songs."

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