"Min" pronounced as "Miwn" as for example in Suratal-Falaq in many recitations that I hear. What is the tajweed rule on this, and how does one form in in their mouth.

Question
"Min" pronounced as "Miwn" as for example in Suratal-Falaq in many recitations that I hear. What is the tajweed rule on this, and how does one form in in their mouth.
Answer
When there is a saakinah or tanween and after one of the letters of the following letters, we hid the .  To do this, we do not touch our tongue to the , and instead get our mouth ready to say the next letter, while letting the sound come from our nose, plus the small sound heard as our mouth gets ready for the next letter.
In the case of surah Al-Falaq, there is a saakinah followed by a sheen, one of the letters which cause a hiding of the saakinah.  We will then read the meem with a kasrah, then without touching our tongue to the gums, we pronounce a ghunnah (nasalization) plus get ready to say the sheen.  We do not pronounce a "w" in this case. 
The only time you would hear a "wow' is if the noon saakinah or tanween is followed by a wow.
For more details, please see:
http://www.abouttajweed.com/the-noon-saakinah-and-tanween/hiding-ikhfa-rule-of-the-noon-saakinah-and-ta.html and the related noon saakinah rule links.