It's a longshot, but I had a similar noise coming from what I thought was the fan.

I usually close the far right vent when there isn't a passenger in the car. Once I opened the vent, the noise went away. The noise was simply the sound of air trying to get through the vent slits.

Hope that helps.

__________________

Current:
2014 VW Tiguan SEL 4Motion 43,000 miles.

2016 Hyundai Santa Fe Sport (wife's).

Past:
2006 Jetta TDI 135,970 miles. Sold Nov. '13.
1995 E-320 Special Edition. 220,200 miles. Sold Sept. '07.
1987 190-E 16 valve. 153,000 miles. Sold Feb. '06.
1980 300-D 225,000 miles. Donated to the National Kidney Foundation.
1980 240-D manual, 297,500 miles. Totaled by inattentive driver.