rah140

I have a 2005 Honda Accord and I just noticed a noise when I first turn on the a/c. It doesn't sound like a compressor clutch or belt noise. I kind of sounds like a flap opening or closing. It only does it one time when you initially turn on the a/c. After the a/c is first turned on and you cycle the a/c on and off, you can hear the clutch engaging and disengaging which is normal. The a/c is working fine otherwise. Are there any other components that can be making this other noise? Is this normal? I am not sure if it was always there and I just noticed it.