Two points should be kept in mind regarding the naming of a child.
1) The Prophet ﷺ counted giving a child a good name among the rights children have over their parents. One hadith states:
عِنِ ابْنِ عَبَّاسٍ رضی اللہ عنہ :أَنَّہُمْ قَالُوْا یَا رَسُوْلَ اللّٰہِ! قَدْ عَلِمْنَا مَا حَقُّ الْوَالِدِ عَلَی الْوَلَدِ فَمَا حَقُّ الْوَلَدِ عَلَی الْوَالِدِ؟قَالَ أَنْ یُحْسِنَ اِسْمَہ' وَیُحْسِنَ أَدَبَہ'۔
Hazrat Ibn Abbas (may Allah be pleased with him) narrates that the Sahabah (may Allah be pleased with them all) said: O Messenger of Allah, we have learned what rights a father has over his child, but what rights does a child have over his father? The Prophet ﷺ replied: The child's right over the father is that he give them a good name and raise them with good manners.
(Shu'ab al-Iman, Hadith: 8658)
Another hadith, narrated by Hazrat Abu Darda (may Allah be pleased with him), states:
اِنَّکُمْ ُتدْعَوْنَ یَوْمَ الْقِیَامَۃِ بِأَسْمَائِکُمْ وَاَسْمَاءِ آبَائِکُمْ فَأَحْسِنُوْا أَسْمَائَکُمْ ۔
The Prophet ﷺ said: On the Day of Judgement you will be called by your names and the names of your fathers, so choose good names for yourselves.
(Sunan Abi Dawud, 2/676, Al-Mizan, Karachi)
2) Good names have good effects, and bad names have bad effects. One narration records the following incident:
عَنْ عَبْدِالْحَمِیْدِ بْنِ جُبَیْرِ بْنِ شَیْبَۃَ قَالَ جَلَسْتُ اِلٰی سَعِیْدِ بْنِ الْمُسَیِّبِ فَحَدَّثَنِیْ أَنَّ جَدَّ ہٗ حَزَنًا قَدِمَ عَلٰی النبی صلی اللہ علیہ و سلم قَالَ مَا اسْمُکَ قَالَ اسْمِیْ حَزَنٌ قَالَ بَلْ اَنْتَ سَھْلٌ قَالَ ھَل اَنَا بِمُغَیِّرٍ اِسْمًا سَمَّانِیْہِ أَبِیْ قَالَ ابْنُ المُسَیِّبِ فَمَا زَالَتْ فِیْنَا الْحَزُوْنَۃُ بَعْدُ۔
Hazrat Abd al-Hamid ibn Jubayr ibn Shayba narrates: I was once in the company of Hazrat Sa'id ibn al-Musayyib when he told me this hadith: my grandfather, whose name was Hazan, came before the Prophet ﷺ. The Prophet ﷺ asked: What is your name? He replied: My name is Hazan, meaning rough and difficult terrain. The Prophet ﷺ said: That is not a good name; I am giving you the name Sahl, meaning soft and level ground where a person finds ease. My grandfather said: I cannot change the name my father gave me. Hazrat Sa'id (may Allah be pleased with him) then said: After that, hardship never left our family.
(Bukhari, 2/914)
This makes one thing clear: names can have good or bad effects on those who carry them. One should therefore choose good names and avoid bad ones. However, a name simply beginning with the letter "N" is not in itself a reason to consider it bad. What matters is the meaning of the name. Moreover, Hazrat Nuh (peace be upon him) and many of the Sahabah (may Allah be pleased with them all), such as Nawfal, Nawwas, Nu'man, and Nafi', all had names beginning with "N", and the Prophet ﷺ never asked any of them to change their names. Some of the Prophet's own descriptive titles also begin with "N", such as Nadhir and Nasir. Many of the Tabi'in and Taba' al-Tabi'in likewise had names beginning with "N", among them Imam Abu Hanifah, whose name was Nu'man, and no one raised any objection to this.
This shows that the belief in question is fabricated and has no basis in Shariah.
Allah the Almighty knows best.
Darul Ifta Al-Ikhlas, Karachi.