Why is it 'dobrou' for good night but 'dobry' for good morning, good evening and good afternoon?
In fact you use an accusative in those greetings. (You can imagine that the sentence begins "I wish you XXX- in accusative.)
And because noc (night) is feminine you have to decline the adjective like a feminine too. So you get dobrou noc..
Den and večer (evening) are masculine and there nominative and accusative look same. .
Ráno (morning) is neuter so you get Dobré ráno.
How is "noc" pronounced phonetically? On my speakers it sounds like "NOTZ" with a short 'o' sound.