Wa'alaik as-salaam!
Brother, I read the book 'The Dreamer's Handbook' a while back and we are encouraged to not dwell on dreams and their meanings. As the good ones are from Allaah azza wa jall and the bad/nightmarish ones are caused by shaytaan(na'uudhu billaahi min sharrih).
But I was really curious so I looked into it(the book)..and Alhamdulillaah gained some benefit from my read.
I went back and checked earlier and in a chapter(Ch.11 incase you decide to read it also) it gave symbols about Birds.
• Predator birds: represent status or rule in accordance with their type and strength. The eagle being the best, followed by the hawk.
• Owl: a thief; weak person
• Crow: evil or deceitful man: liar
• Chicken: a blessed woman
• Rooster: A caller to prayer
Now a peacock wasn't on the list and we can't really add it to the predatory birds'. But i found on a site that it symbolizes Pride and world vanities.(oh oh)
Them we have the cage. On the same site it is said to symbolize 'prison; house', basically something closed-off.
And they said dreaming of a bird(not exactly a 'peacock') inside a cage means, sickness will befall one's son. And a bird flying away from its cage stands for one's death...
Remember though, their was no proof/daleel(a hadeeth or a fatwa of an 'ulemaa) indicating this to be the correct interpretation.