Lowering noise levels on P180

[Things change I've changed]

to get good air flow in my P180 I have the rear fan on full, the thing is tho the noise is really bugging me, it sounds like it's the air being pushed throw the vent more than the motor, do you think it's worth cutting the vent out as i'm sure it will cut the noise levels down dramaticly, it's only a 2min job.

does anyone else notice that the air flow in these case's really ain't that good, if I take the top filter out the front of the case it takes nearly 10 degrees off my cpu, i'm temped to leave the filter out really.