Cross-fading creates short noise

Several parts where I used crossfading has very a sharp noise. It's very short so barely noticeable but I still need to find a way to get rid of it. 

Does anybody know how to fix this?
I'd appreciate help thnx,

cksh.simon
Does anybody know how to fix this?

Yes. Post a screenshot of the splice, zoomed in close, and I'll bet we can tell you what the problem is. Actually, we probably won't have to, because it'll likely become obvious when you look at it closely.
 
If that doesn't reveal the problem, try muting both clips you just crossfaded and solo the track. If you hear the click, then it's a leftover fragment as Craig suggested. If you don't, then it's just a bad crossfade.
 

Even though it's a good practice, it isn't actually technically necessary to split at a zero-crossing if you're doing a crossfade, only if you're doing a hard splice.
 
The definition of a crossfade is to gradually reduce one clip's level as the other clip's level is raised. Because the clip samples don't suddenly jump from nothing to something or vice versa, you won't get clicks. Even if you snip the clip at a totally "wrong" spot - as long as the fades are of sufficient duration, which worst-case need to only be > 12.5ms.
 
Back in the day, we'd cut tape at an angle for the same reason. But if you didn't have enough room for an angle cut, you'd have to do a lateral cut, which could only happen at a place of silence in order to not be audible. It's the same with digital audio. Except nowadays we get do-overs.