Heres a strange thing.

Not a problem just an observation, if anyone is interested.

The fans in my Antec P180 case are set up like this:

In the bottom chamber I have a 120mm fan midway drawing air in from the front out the back via the PSU. In the top chamber I have a 120mm inlet fan at the front and a 120mm outlet fan at the back, the top hole is blocked off (all 3 fans are on the slowest setting).

I noticed that I was getting a bit of dust around my optical drives so I figured I must have a little negative pressure. I don't like dust in my innards so I thought I'd experiment with turning off the back fan.

Now the strange bit, by removing the back fan, the front one became noisier. I'm certain that it's not due to the electrics as they were wired in different places, so I can only put it down to some sort of internal pressure.

What do you guys think

It is working harder as now the case is pressurized.

Normal from my experience.

Train, that's all It can be, but it's amazing that it makes that much difference in such a big case.

It's not the size of the case that matters, it's how you use the holes. (I couldn't resist :D ). The volume being filled doesn't matter if it's already full (in this case with air) -- any more air being pushed in has to displace the same amount. Otherwise, pressure inside the case increases and causes back pressure.

A friend of mine had the same problem when she had a whole house fan installed (which cools the house by blowing the inside air into the attic, where it's supposed to escape through the numerous gable and eave vents). It couldn't get out fast enough, and some portion would blow back into the house though ceiling light holes and other gaps, bringing with it all the detritus from the attic. She added a fan at the gable vent (blowing outward), and the problem stopped.

prouton, my holes are all perfectly formed :D

I perfectly understand why it happened it just seemed weird that it would make such a difference in a large case with a hole at the back as big as the front fan, but there you go science is a funny old game.

Install a rheostat [fan speed control] on the back one. A little experimenting should find that happy rpm where you are pressurized and the front fan is not laboring.

Train that's a good idea, the fans that I have already have a three speed switch but that would give me a more accurate control.

A fan controller is a great way to fine tune the fan speeds/noise/cooling needs of your computer. I have this one. http://www.jab-tech.com/Sunbeam-5-1-...r-pr-2529.html

Along with my 120mm S-Flex fans which were already quiet, but when turned down just a little become almost inaudible, I have the cpu fan hooked up and also turned down some...which makes my system almost silent...just the quiet "whooshing" of air.