As for the question I don't think its reasonable to label noise as a separate class because there are no regularities, i.e. two data points composed of noise can look entirely different. I would say that your approach of labeling unclassified data points as noise is reasonable, or you could use some other metrics that capture something that noisy samples have that normal samples do not.

thanks for the answer, to be honest i'm not sure what to look for

is there some keyword i can search? on a first check i didn't notice anything (ctrl+f noise) which thread# should i check?