HOW??

[huggable]

More noise usually appears in high ISO pictures, but you're be surprised that incorrectly exposed pictures generate noise too!

There are third-party software to remove noise, try Noise Ninja or Neat image.

 

[spidey89]

It would seem to, on wide angle lenses, probably barrel shaped ones will capture the hood, think of it, the petal shape ones seem to go inwards when locked properly are the corners, whereas the barrel is the same throughout the rotation, probably why barrel hoods are not included with wide angle lens and will occur even if not locked properly