Why is there audible noise in the inductor of a boost converter?
When the current through the inductor changes, the magnetic field does as well. This magnetic field causes a small attraction/repulsion action in the coils of the inductor, which manifests itself as a vibration, aka sound. You may have noticed that some CFLs and LED lightbulbs have a high pitch whine, and many mains transformers have a low hum at around 50/60Hz for the same reason. 


  Is that noise dangerous for circuit


Not strictly speaking, it's just sound after all. As long as you are using your parts within their specifications, all should be fine.

You can mitigate this phenomenon by increasing your switching frequency or potting your inductors in an epoxy of some kind, much like many SMPS have.