Opened Vent to Inspect Smell, its Wood!?

[RapaNui]

Hey everybody, here's something I didn't expect. I opened a vent in the bedroom, because it's had a bit of a smell. It comes and goes. Stuck my phone in to take a photo and realized its wood!

The bottom of the image is actually the metal duct work. I can't seem to find any opening around the vent I removed. I'm fairly certain we're just smelling the wood. Doesn't look to be in too bad of shape, just dusty. Should we just block this vent off? What in the world would it's purpose be? Other vents that I have opened are metal and the smell doesn't seem to be anywhere but the bedroom corner.

Thoughts?

 

[WorthFlorida]

That is the cold air return to your heating system. A very common practice at one time and I'm not sure if it is still done that way. I had a house built in NY in 1987 and it was done this way.
If you turn on your FAN at the thermostat you should feel the air being pulled in. This was also done in basements. The sill plate was cut out through the floor into the joist cavity. Then sheet metal was nailed down the joist to the air handler before turning into 100% duct work. The other rooms with metal may be the supply side or returns. All depends how the joist are situated for the room. Registers near the outside walls, usually under a window are the supply side.