Hissing Noise When Defroster is On

[5050punk]

Hey Guys,
I have a 96 4Runner. It's been having an issue where when I turn the defroster on, I hear a hissing noise coming from the passenger footwell. I only hear it on defrost though, not on any of the other air settings. I also only hear it when the car is running.

I don't see any specific hoses or anything loose in the footwell. I tried checking in the engine bay with the car running, but it's too loud to hear the hiss. I took off the glove box, and the thing arrowed below seems to be the closest to the sound, but I have no idea what this is.

Any ideas?

 

[Shoke]

Thats wear the Blower Fan is.

You can see it here.

4Runners.org - Cleaning Your Interior Fan Unit

 

[Qyota]

On the defrost setting, the A/C is on, so you're hearing the expansion valve. It's normal. Mine usually fluctuates in intensity, but it's always there if the A/C or defrost is on.

 

[5050punk]

Thanks guys. I'll give cleaning it a try.