Reviving an old thread, I've had a rattle that I was convinced was the vents, 3 months this has been going on for!
So I removed the leather dash insert that the vents are mounted into, open the glove box and gave it a good pull it then all starts to come away.
There is one wire to the hazard lights disconnect this.
Then take it out of the car and hold it in your hand give it a good shake and it sounds like the vents are rattling, you will notice white retaining clips that have movement on a couple of them, they come off if you gently pri them, take them off and use some double sided trim tape, the 3m type for spoilers and so on, cover the black molded pointed part. Then place the white clips back on, just for good measure mazda have applied small strips like an adhesive fabric to areas that are rubbing points on the outer edges of the trim, I applied some more thin cut down strips over this and put everything back together. It's now much better..... no rattles!
Don't fool yourself into thinking it's the vents
Hope this helps some of you
Mark