stop downloaded sound effects from going to itunes

I use unity (a game engine) to develop games. When I download sounds to use in those games, They go directly into iTunes and clog up my iTunes music feed. I am downloading them from outside sources, like freesound.com and others. I have tried making a playlist to put all the sound effects in, but they stick around everywhere else.

Two questions:

1. Is there anyway to make downloaded sounds not appear in iTunes by default?

2. If I delete the sounds from iTunes, will they be deleted from my computer altogether, or just from showing up in iTunes?