My iMac has made a new noise recently....

hoover nozzle

 

meh that's what i'd do. Can't see there being a problem using the hose and nozzle from a hoover. As long as your hoover isn't powerful enough to suck a golf ball through a garden hose

 

There are probably instructions to clean it on the Apple support site.

I'd just open the case and take an office cleaner and blast it from the inside-out. Instructions on how to open the case are online.

 

You deserve to have a noisy computer because you own a Mac.

 

I use a can of "Dust-Off". It's just a can that shoots out brust of air and it doesn't harm your computer at all. It works very well for me.

 

I use a vacuum cleaner (while the computer is switched off). It may be more than you can see and that the vacuum will get though. If you know what you are doing it would taking it apart and cleaning the heatsink as well as the fan.

 

if you have one, try anti-static

 

ahhh but surely that just pushes a lot of the dust further in to the comp

 

not really, you just have to open the case outside and make sure you get all the parts clear.