Is it just me or does it is there and extra sound between Mẹ and của. I always get this one wrong because Mẹ just doesn't sound right to me (I live in Vietnam so this one of the words I recognise easily usually)
Me too, and I've just heard "Ma" some times (easier to remember it means "mom")
There is a vocal glottal fry at the end of the vowel that has the dot under it. The dot is called (nạng). It could make it sound as you said, perhaps, depending on the vocalist. Perhaps you would benefit from reading the section about how to read and pronounce vietnamese characters. Hope this helped.
The word ổn doesnt seem to be pronounced in the correct tone...or is this a case like cảm ơn being pronounced as cám ơn?