Thought this might be worth sharing for those who have been plagued by a noisy Mac Pro tower.
The fan noise from the Mac tower (around 4 years old) in one of our edit rooms was getting increasingly noisy, but as with everything that changes gradually over the years I never gave it much thought.
Finally I thought 'This is getting ridiculous', took off the side panel and found that the video card was very hot to the touch (no, I didn't poke my fingers into the electronics, just the plastic fan ducting). I was surprised because we periodically carefully clean the dust from the Mac to avoid problems like this.
It took a quick internet search to find the solution. The hidden fine cooling fins on our video card (ATI Radeon X1900) were completely blocked with around 4 years of dust, though it was impossible to see this whilst the card was plugged into the motherboard as they're shrouded by a plastic fan duct. The solution was to carefully take the card out and use a paintbrush to clear the dust from the fins, together with a fair amount of blowing.
Now the card is running at a normal temperature the fan is really quiet again and our editors can sleep undisturbed.
Just be careful to make sure you're grounded so that the card isn't fried with static.
Yep that'll do it. I generally clean that vent out every 3-4 months. My tower is up off the floor so it's not so bad, but if your tower is sitting on the floor or carpet, you may have to check it more often.