PC Desktop Case Fan Making Weird Noise

So I got my new 80mm case fan in the rear of my PC. It's NOT rattling like I originally thought, but instead, it makes sort of a strange, friction noise. To test it, I had it on, and I held it in my hand. It just made the "whrrrrrrrrrrr" noise. As I slowly moved it closer to fan spot in the cage, a sort of friction-like noise got louder and louder... as if the air blowing out of the fan spot was hitting the metal grid on the cage, and I could hear it...

I can only hear it if I put my ear up to it. I'm just wondering... is this normal? Someone please tell me it's normal. Like I can HEAR the air hitting the cage... it's not just this fan, I tried it with others and in different desktops and it makes the same noise. This is all normal, right???

Yes, the fan is blowing OUT of the desktop, it's not SUCKING IN air.