EXS 24 Logic Sampler Users Group

I assume you're talking about the audio problem with the G5.  This problem is pretty 
common actually.  I've heard that there are people that don't have it... but I have no idea 
how wide spread this problem actually is.  However a huge number of pro audio people 
are all complaining about the same problem on the official Apple Disscusion board.  
Anyway, here's the break down.

There is a really weird high pitched digital screetching noise.  The noise sounds like the 
volume is related to CPU activity.  It's loudest when the you switch windows with Expose or 
scroll windows.  And kind of chirps at about 1Hz when the CPU is idle.

This noise also leaks through to the audio outs.  And the really weird thing is that it even 
leaks to audio outs of fire wire audio devices.  I don't know of this happening first hand 
since I don't have a firewire audio device, but a lot of people with MOTU 828's and Digi 
001's say it does.  Another problem is that the noise leaks to monitors that are grounded 
to the same power source.  I havent experienced this either, since I live in Japan and here 
there is no third prong on the power cord for the ground (just like a little wire... but since 
the only ground source in my apartment is in the other room, I don't have it hooked up).  
So basically none of my set up is grounded.

As to what's causing the noise, most people say that it's some kind of ground loop caused 
by the power supply.  Apple is already on Rev. E for power supplies just because of this 
problem.  Its not totally fixed yet, but I've heard that Rev. E is an improvement.  Apple is 
being really shady about the problem though.  They already closed the biggest message 
stream on the official Disscusions page, and most AppleCare people often deny people's 
complaints.

There are some kind of band aid fixes though.  One is a software solution called CHUD.  
CHUD is a bunch of tools for developers made by Apple.  Its not included with OS X but 
you can download it from the Apple Ftp pretty easily.  Anyway there is a feature where you 
can edit CPU settings.  If you disable something called NAP (which appears to be some 
kind of idle process) it cuts down on the noise a lot.  But it doesn't remove the noise 
leakage from the audio outs.  For that, you need a device called a Ground Loop Isolator.  
These can be picked up at any Radio Shack and sell for like $12.  I had a friend mail me 
one from Seattle (since I couldnt find any here).  For fire wire audio outs I've heard this 
works too, but I think you would need one for each out.  So like for the MOTU 828 you'd 
need 4 Ground Loop Isolators (they come in a  stereo pair).

So thats the big problem.  I have one of the first Dual G5's in Japan.  Acutally this is my 
second.  The first one I had a huge problem with the fans and had to be returned.