Extremely noisy fans

Not right.

Reset the SMC - unplug for couple hours all power and cables.

Something is wrong and take it in. They normally are quiet.

I've seen such a problem with underpowered UPS a couple times, there may be other causes. Even migrating from a G5 to Mac Pro causing Mac Pro to misbehave.

One reason to run it for awhile before making changes, and even run Apple Hardware Test also.

Optical drives are noisey. Maybe whatever the FW device/cable is what you need to change. Even look into another optical drive or get a 2nd for lower bay.

So then look at the audio. FW cables aren't shielded, well, most, and one reason to never ever mix audio or consumer devices along with hard drives on FW.

There are people extracting (Pacifist) and using Firewire IO drivers from 10.5.8, I think you need the whole "family" of 8-10 extensions.

You'd have to buy Ref'd Specials to get Leopard. There is no option or choice, no window, and no 10.5.7/.8 DVDs. So yes, you have the picture, I thought it was an anomaly the first time, but "3's the charm" - or about 6-9 months. EOL is actually perfect time to buy.

Confirm? you're kidding, right? no? well, they never confirm anything.

I started thinking I'd wait; that they'll get it together; bad timing. Now? I actually prefer using Windows 7 and building a PC to spec. Thought I'd use SL on my Mac Pro but no way, no thanks. 10.6.9 anyone?

I have the exact same problem:

a brand new Mac Pro 2.66 Quad-Core used for professional music applications, and my fans get incredibly loud that it's pathetic and almost useless in a music studio.

Here's exactly what happens:
Once the computer boots up, regardless of what's plugged into it or what it's doing, (even if nothing is plugged in and it's doing nothing), within 35-40 minutes, the PCI fan gradually spins up to 4500 RPM, and the Power Supply fan spins up to 3500 RPM. Only shutting down and restarting will reset the fans to their normal speed. Basically, I have to reboot my computer every 45 minutes. Not good.

Here's what I have tried, multiple times each:
Apple Hardware Test: no problems found.
Unplugged everything, let it sit for an hour, and restarted: same problem
Manually reset the SMC inside the case: same problem

I am absolutely at the end of my rope with this computer. Does anyone have any advice?

OK... the problem is isolated to ANY audio playback on the 2009 Mac Pro. This occurs 100% in SL or Leopard. Any audio playback causes the problem.. iTunes, Quicktime, VLC, Web, VLC. etc.

The fans are a byproduct of *Excessive HEAT* Your CPU's are being fried at temps equivalent to 100% load.

My temp goes from 31(c) to 60(c) - almost 30(c) doubling the temps in a couple minutes. Ive had a MacPro since 1,1 in 2006 that was sold off to buy the 2009. My 2008 at the studio does not behave like this at all...

Please install iStat Menus. This will let us see under your hood with the temperatures of CPUA. Lets see how for yours gets!

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Kick the fans up to 900 rpm seems to be where I start to notice them slightly but keeps air going enough. Nehalem processors will kick up 10-20*C from almost any operations or tasks. Even running 12 copies of memtest.

We can always kick the fans up to keep the temps down... But i'm used to a SILENT MacPro and would like to keep it that way... Like most users...

That is why I said it is just barely audible. I think the video card fan is what I tended to hear, depending on which (at one time I had the fanless 7300GT, the price you pay is performance etc).

Silent doesn't usually go with high performance; forget external storage array or anything, and maybe a custom water cooled (but not in the G5 tradition!!)

People complain about the case humming; or the metal grill 'cause they can hear the front drive. The optical drives? terrible noise when in use for most.

Ever use a laptop lately? the fans have to work hard. I use to put my system in a small cold room and run 15 ft video extension and USB extension. THAT was quiet, too.

I can't tell if the fans are in the 800 rpm range, and what I said was around 900 was where they became audible. Use that and play with SFC a bit.

Thanks for providing the details. Those are off the chart!

Enough so that other than SMC RESET overnight, and running AHT, they are more than reason enough for an appointment and likely motherboard replacement or something.

People have even gotten graphic card replaced when its fans were louder than normal.

You want that looked at and dealt with and serviced by Apple.

As long as people follow the directions for performing a SMC reset.. It only takes about 15 seconds of being totally being unplugged from the power. The important part is... Plugging the Power in before anything else.....