"Squeak"? noise behind dash

2004 Prius base
191K miles
Just curious if anyone knows what this is. There is a squeaking (for lack of a better term) noise from behind the dash..

this may seem childish but this is the closest noise i can compare it to. Soda Popinski's laugh in Mike tyson's punch out.

1)it's only present when climate control is on.
2)it's present in winter or summer
3)it's present if the car is in motion or parked.
4)performance is not affected(other than my MPG being abysmal(~40)but after going from Kroger gas to Chevron it's back up to 44(i attribute the other 5 to non LRR tires))

it's not a pressing issue(i hope not at least) because there are no codes, the car doesn't overheat, there is turbulence in the reservoir so i dont think it's air in the coolant.

Any ideas? Just trying to keep it running in good shape, only other issue is the catalytic converter (these squeaks were present before any CEL were on reguarding the cat.)

Thanks in advance

 

havent' thought of that. i will give that a try on the way home.

 

ha. I work for an airline so i get a lot of airline jokes. reminded me of this email i got one time reguarding the Quantas gripe sheet, basically it's a sheet the pilots fill out if there's something wrong with the plane.
P=Problem
S=Solution

P: Mouse in cockpit
S: Cat installed

 

It seems to be the flap for air recirculation. If I press the button to recirculate the noise goes away. If i press it again for outside air it the noise doesn't come back. At least until i turn off and start the car again.

Thanks alexeft and Eclipse1701d. I was afraid it was some kind of heater core problem