I've never seen Nicky try to fly. But that doesn't mean he hasn't tried, because I don't spend enough time in the tack store or with the bird that I easily could have missed his flight attempts. lolOh wow well that's definitely good then!! Lol so he's never even tried flying or anything? Wow. Probably for the best though. That's neat he can wander where he wants though.
But aw yeah, it does seem like he has a pretty laid back life but like you said, he probably wants his own person and/or more attention and that could be his problem. That's good he doesn't seem stressed though! Does the screaming usually happen when someone isn't in there? Or is it all the time? Cause a lot of parrots especially rescues learn through previous experience that screaming their heads off will get them attention, negative or positive, that they want, much like kids, so they'll do it when they want attention. And then the owners either give it or go yell at them or whatever and thats still attention. I saw a great article on training them out of it once but of course now I can't remember the site and it's probably a lot of work. But basically it involves extinction principles and training a new behavior. Extinction is really hard because you have to be 100% consistent, even once every hundred times they will try again, same for any animal, but it's really effective. It's just what it sounds like, never ever ever give him attention when he does that. Then once he's better with that or during you'd start rewarding something else. Such as a nice word if he talks or going to get you or whatever instead of SCREAMING lol and the idea is they will do that instead of screaming. But obviously it's hard especially if you're on the phone or dealing with a customer and especially if he's not even your bird to begin with.
How often is his owner there? He needs quality time with them I think. And perhaps more toys? Something to do?? Can they not take him home?
And awww that's awesome!!!! What happened to him? Did your roommate take him?
But yeah, you're absolutely right that most thrive on attention and a bond with their special person!! And yeah, they usually do bond with select people. Or sometimes they will be very friendly as babies then the hormones and teenage phase hits and they're attacking everybody. Also that's another reason why rehoming and rescuing them often has issues. They get very attached and rehoming, especially if it's very often like say getting rehomed only to be returned because of a behavior problem only to be rehomed and returned again, etc., takes a toll on them and the more they're rehomed the more it affects them. So yeah, I definitely think Nicky needs his one person. I know you don't own him but if they don't already, I would try to talk them into coming and visiting Nicky more often and see if they would be willing to take him home. Or at the least buy more toys
His noise making happens when he wants attention, I know. Things like, if staff is eating lunch, he gets loud because he wants his share. Most of the time he gets a snack, so it totally works for him. Or, he'll alert us when the phone rings. If you don't answer the phone right away, he just gets louder.
Training him out of that behavior will probably never work in this environment. There's no way we'll ever get all our staff and volunteers to follow the training program. Then there's the occasional visitor that goes and talks back at the bird when they hear him.
We're his owners now, his previous owner gave him up. We've tried to get one of our tack store workers to take him home, because he really really likes her the best, but because of the other pets she already has in the house, she can't bring in a parrot. I've tried talking to the rest of our management about finding Nicky an appropriate home, but because we're a rescue farm...our President feels like this is the best home for the bird.

My roommates parrot, Hercules. She was planning on moving to Texas a few years back, she had her house on the market and everything pretty much packed up and ready to go so she gave her three parrots up. She didn't think she could facilitate their move also. After the birds went to their new homes, she got cold feet and never moved! lol But I know Hercules went to a super home, he's very happy there. A woman that works at a local feed store took him, so anytime I go to the feed store I ask her how the bird is doing. That worked out great.