I read it in a letter where the girl was signing it off. The rough idea I get but I want to know what does the extra 'noch' do to the overall meaning of this fragment.
In spoken language, it is used, when a talk is cut short: There wasn't time to talk extensively about the person concerned. But the person should at least be greeted, so the greetings are "added" to the end of the talk.
I haven't seen it used in a letter and wouldn't do so, because it looks as a PS with important content. One get's the impression that the writer didn't think about the letter in before hand or had to short cut the letter due to time limitations.
This usually is rather used in colloquial speech, when you tell something in the last moment.
For instance when your friend is talking on the phone and while he is finishing the talk, you want to pass greetings to the one on the phone, saying:
Another example would be
It is not neccessary to give the auch here.