what is brown "stuff" coming out of front center vent? falls apart when touched on 2000 Toyota Sienna

this brown 'stuff' looks a little like insulation of some sort. also when fan is on high, there is a loud humming noise/vibration with ac or heat. noise seems to be up front on passenger side. sounds like coming from under dash. ??

2 answers
MICE HAVE BUILT A NEST IN BLOWER HOUSING NEED TO CLEAN IT OUT.
PROB. NEED MECHANIC. THIS HAPPENS A LOT TO MANY AUTOS.
SEE IT OFTEN IN THE SHOP. WITH FOREIGN MATTER IN FAN BLOWER WHEEL
WILL HUM AND VIBRATE WHILE PUSHING STUFF OUT HEAT/AC DUCTS.
or foam on duct connrction is starting to fall apart