Mysterious Problem solved
 

Within two weeks of purchasing a new Hyundai, a strange event
occurred. When the fan was on, bits of foam and straw flew out of the
vents. We took it back to the dealer, in a huff, as you can imagine.
They found that a field mouse had chewed its way into the ventilation
and built a nest.

We set a few traps, and the mouse house problem never reappeared.

Moral - don't rush to blame others before all facts are known.