When the letter Noon (ู) has a sukoon (no vowel) or when tanween occurs, four rules apply:
Letters: ุก ู ุน ุบ ุฎ ุญ (throat letters)
Pronounce the noon clearly without ghunnah.
Example: ู ููู ุขู ููู โ clearly pronounced noon.
Letters: ู ุฑ ู ู ู ู
The noon merges into the following letter.
Example: ู ูู ููููููู โ noon merges into ya.
Letters: Remaining 15 letters
Partially conceal the noon with light nasalisation (ghunnah) for 2 counts.
Letter: ุจ only
Change the noon into a meem sound with ghunnah.
Example: ู ูู ุจูุนูุฏู โ noon becomes ู sound.