As per people, letters are different. You find some people are quiet, other are loud. But regardless of this, there are places when even the loud ones must be quiet! Take for example, the library or art gallery.
In Tajweed there are rules regarding the silent noon. This is known as “Al-Noon Al-Saakinah” in Arabic. The rules regarding the silent noon also apply to tanween .
Rule One: Ith-haar Al-Bayan (where the noon/tanween is pronounced clearly).
It’s pronounced clearly only when the following is true:
The noon has a sukoon on it (نْ) and one of the following letters come after it (whether in the same word or following one):
alif, haa, khaa, ayn, ghayn, haa
هـ غ ع خ ح أ
Note this also applies for the Tanween.
Examples of this are as follow:
example one: hakeemin hameed–حكيمٍ حميد
example two: an aqeemoo – أنْ أقيموا
Please note that I have put up very beneficial documents under the “resources” page. I hope these are of benefit.
– Tanween [Gateway to Arabic: page 40]
[Tajweed Basics: Foundations and More: pages 11 – 14]
– Sukoon [Gateway to Arabic: page 48]
 – noon: the 25th Arabic letter, that makes a “n” sound, such as in the words, “n”ear, “n”or, A”nn”. The letter in arabic is written as ن
An interesting website all about the letter noon is here: http://www.meem.freeuk.com/Noon.html
 – The tanween is an “n” sound added to the end of the word in certain circumstances, usually it functions just like the “a” and “an” in English, indicating an indefinite article. The word tanween, usually translated as “nunation”, means “to ‘n’”, or “‘n’ing”, making an “n” sound. There are three types of tanween:
1- fat-ha tanween
2 – kasra tanween
3 – damma tanween
fat-ha tanween: The fat-ha tanween is pronounced “an”, as in “animal”.
kasra tanween: The kasra tanween is pronouced “in”, as in “in”, “tin”, “fin”, etc. Some native Arabic speakers might indicate a kasra tanween with an “en”, thinking that “e” sounds like the Arabic “yaa” letter. This is a mistake that stems from not knowing how native English speakers pronounce the “e” sound.
damma tanween: The dhamma tanween is pronounced as a short “oo” followed by an “n”. This sounds like the short “un” in “uno”, not like the long “oon” in “soon”.
tanween at the end of a sentence: If the tanween is the last thing in the sentence, it’s not pronounced. In the case of a fat-ha tanween, the alif is pronounced as a long vowel.
 – More about sukoon can be found here: http://en.wikipedia.org/wiki/Arabic_diacritics#Suk.C5.ABn
 – More about these letters can be found here: http://www.meem.freeuk.com/ scroll down to the “ABJAD TABLE” and select one of the abovementioned letters to learn more about it.