Ian,
I don't know for sure but I would say that the squeak coming from the vent is not the Plasmacluster. I have just under 1500 miles on mine now and there are no rattles or squeaks what so ever. I even had the dealer put the Sirius in which I thought may induce some rattles when the tech pulled the dash apart to install it. I wish I had a camera phone with me when the service manager walked me back to my car to ask where I wanted the antenna mounted; the whole right side of my dash was apart.

The one thing I did have a little episode with was the center console. I realized that I had put a pen and a sharpie in the little tray inside the center console and because it’s not padded or anything the pens would just roll back and forth and rattle with bumps in the road. I cut up an old mouse pad to put in the bottom of that tray and now the noise is completely gone.