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