Scratchy scratching type of noise coming from HVAC vents

I had the heat on today. I had circulate air on as well. I then parked and turned off the heat completely. Powered off heat/AC unit, but car was still running. After a few seconds I noticed a light scratching type of noise. At first I thought it might be a belt or something, but I have a feeling it's coming from the vents for some reason/how. It seemed to come from the right side and center at first. Then even on the left side of the dash. I just bought the car and it has less then 1,000 miles. Am I being paranoid or what could the noise possibly be?

Thanks,
Steven M