My beloved GCC has been super bipolar for the past 7 months. He shreds the papers at the bottom of his cage, and dwells around down there like a little monster, bashing into the side trying to bite, and making grumbly noises. He screams non-stop. He is the worst when he is in the "bird room" where I also have a large cage of budgies. I roll his cage out of that room into our livingroom, and all he does is try to get into the bird room and scream for the budgies.

He is obsessed with the budgies, but he can't hang out with them because he hates one of them, and he has injured her beak in the past. 

Basically, if he is in the bird room, he screams and/or is an aggressive MONSTER in his cage. If he is outside the bird room, he is trying to get back in there and is calling to the other birds. For a very small amount of time, in the evening when the budgies are quiet, he will let me snuggle him and be my sweet baby again. 

I don't know how to handle his cage agression and obsession with the budgies. 

Details: He is 5 years old. He gets a ton of attention and out of cage time. He eats healthy, has a million toys, has a nice cage. He has no reason not to be happy other than I won't let him bully my budgies. 

What's wrong with him?

HELP! I AM DESPERATE FOR ADVICE!