I have the same thing and it sounds metallic. I hear it whenever I drive over a rough patch of road or railroad tracks. I thought it was my keys rattling but its not. Not sure what it could be.

 

I get the odd rattle here and there (plastics in the cabin), but it never lasts long or for any significant duration. I have to say that I broke her cherry today in the snow/ice. I have highly touted winter tires and I must say that this thing is an absolute warrior in winter conditions with proper tires. I fell in love with it all over again. Oh my, she owns the winter roads.

 

I would have thought the same thing but it does it when I let off the gas and let the car slow down through the 2500 to 2000 range. On acceleration she is perfect.

 

Oh that, I have that too! There's no real defined range. It seems to happen when he clutches are engaged (or partially?) engaged. Beacuse when the clutches are disengaed while coasting, it's smooth.

 

Let me preface this with: I hunt snakes/gators on logging roads, beach fronts, and back roads. Quick turning, braking, and reverse in sandy, dusty, or sea-spray environments. The car isn't abused though, as oil is changed, corrosion-x, and fresh water rinsing are frequently utilized.
At 36,000 miles my idler pulleys (plastic) were worn badly. This caused the new serpentine belt to ride off track. By off track I mean, the belt would drift off the accessory pulleys and end up riding with only 1/2 the belt grooves through the circuit.
If the belt partially separates lengthwise, the 1/2 not riding on the pulleys will whip around in your engine bay, and you will more than likely lose a/c or power steering hoses.
I would highly recommend upgrading the (2) plastic idler pulleys with their steel counterparts made by Hyundai. The Hyundai part number is 25287-2C000. You will need 2 of these. The tensioner pully is the same diameter but I didn't fool with it, as I was unsure if the left hand thread counterpart was similar enough for the swap.