Noisy air vents

[Mussels]

It's that time of year again and I'm trying to make the house cooler when there's no breeze to help. I have a 6" inline fan in the loft and it connects to a 6" vent in the loft hatch, it pulls air through the house and into the loft and cools everything down quite nicely.
The fan is quiet but the noise of air rushing through the system is not and I suspect the cheap plastic vent is largely to blame. Before I buy ten random vents in search of the grail, is there something I should be looking for in my searches? Do I just need to fit 2 vents to spread the load or is the problem nothing to do with the vent?

[crust]

Anytime you're moving air through a restriction you'll get some noise. Post a picture of your current vent, I may be able to recommend a better one.

[Mussels]

Here it is in all of its cheap plasticy goodness.