Hi, It sounds like Buddy is trying to talk, Casey started mumbling first too and then it slowly turned into words.
Casey is almost five months and she learning words really fast, I think.

She started when she was around three months, but it is different for all birds.
Most of the words aren't super clear but they are recognizable... like Hi Baby, Peek a Boo, Hi, Hello, what cha doing, bye... anothers she is still working on, like "Where's Casey" when we play peek a boo, and so far she has "ere's C eeeee"!

And yesterday someone in the house said we were out of vanilla and Casey from the other room yelled "Vanilla?"... again, it wasn't super clear, but it was definietly vanilla!

So it shows that they don't always need repetition to learn a word!
Any day now a word will just pop out of Buddy's mouth, and you'll be super proud! Especially since he is mumbling and getting prepared to talk! Just keep talking to him and make everything sound exciting! Just remember that all birds, like kids, are different and they will do it when they are ready...

Okay, that is probably more than anyone wanted to hear, but anywho... Good Luck!