Apprehension...
I'm not very familiar with Amazon-specific sounds/verbalizations, only the little interaction I've had at the rescue I work at. However, i agree that just on a general "bird sounds/motions/actions" scale, it also looks to me to be the very common, typical, universal sound/motions of "Apprehension".
And honestly this makes perfect sense, because you've only had him for what, a week today I think? He's not at all settled-in yet, he's not taken "ownership" of his new cage/toys or his "area" in-general, so he has no "safe-space" yet, or territory that he feels comfortable and secure enough in to take command over, and of course in only a week he hasn't bonded with you or anyone else in your home yet. So he's simply feeling very insecure over-all right now, which is to be expected.
He's going to be "Apprehensive" of pretty much anything and everything for a while, and as Sailboat said, you need to slow-your-roll a little bit when approaching him or his "area". Yes, he's still stepping-up for you AFTER his initial "guardedness" has gone away, but when you first approach him at any point during the day, especially first thing in the morning after he's been sleeping, he's going to be very nervous and "guarded". Once he settles down and realizes that it's the same person that has been with him all week, then he's probably fine, or as fine as he can be after being in a totally new home with new people for only a week, lol...
This is just an apprehensive "Whoa buddy, slow your roll there" reaction. After only a week, you're lucky it's not 'Zon beak to the face...You really are making tremendous progress with him after only a week. But you have to remember that while you're feeling excited and happy about him being there, and you want nothing more than to just love the little guy, your immediate enthusiasm does not mix well with his current feelings of insecurity about everything right now. So you just need to remind yourself that for him right now, this isn't the happiest time of his life, and he's not feeling the enthusiasm that you are about him being in your home, he's feeling insecure and unsure about everything. He's obviously figured out that you're probably not going to hurt him because he's stepping-up for you, but he's still doing it apprehensively as of right now...
****So just try to slow yourself down when you approach him, or even when you're simply walking into the room he's in. Something that you might try first thing in the morning, and then any time you come home after being out of the house, or even every time you're in a different room from him and you're going to enter the room that he's in, is to start talking to him gently BEFORE you enter the room he's in, BEFORE he can actually see you. That way he'll know you're coming long before you enter the room and before he can see you. And then keep talking to him softly, gently, lovingly once you enter the room that he's in and throughout the entire time you're approaching him and/or his cage/area. And if you're approaching him because you want him to step-up for you, then rather than just reaching your hand out and asking him to step-up, keep continually talking to him up until the point you are approaching him and/or his area, and then COMPLETELY STOP MOVING TOWARDS HIM BEFORE YOU REACH YOUR HAND TOWARDS HIM OR ASK HIM TO STEP-UP. So start talking to him lovingly and gently long before you enter the room that he's in and long before he can see you, so you are letting him know that you're going to be entering the room he's in, then once you enter the room that he's in STOP in the doorway/entrance-way, where there is still a good amount of space between you and him, and just stand there at a distance from him for a minute or two and continue to talk to him gently, and while you're standing in the doorway/entrance-way of the room he's in, actually TELL HIM that you're going to walk over to him and that you are going to want him to step-up,
before you get anywhere near him. It's always a great idea to tell your parrot what you are going to be doing BEFORE you do it. Then very slowly walk over to him/his area, talking to him gently the entire time, and once you get right in front of him,
at the place where you'll be when you ask him to step-up, STOP! Simply stand right in front of him, keeping your hands down, never moving them at all, and then stand there right in front of him and continue to talk to him for a minute or two, and tell him that you're going to ask him to step-up for you BEFORE your hands even move. Then after standing right in front of him and talking to him for a minute or two, telling him you are going to want him to step-up for you, THEN you VERY SLOWLY raise your hand to him with your finger out-stretched for him, talking to him the entire time,
never stop talking to him or telling him what you're going to be doing or what you are doing. This should make him feel a lot less apprehensive and anxious about you in-general, and hopefully this will quickly result in him stopping these apprehensive and guarded sounds/movements, and should also help to get him to step-up for you without any nipping or biting, because he'll know that your coming before you "just appear",
he'll know you're going to be walking across the room near him and his area, and he'll know that you're going to be asking him to step-up and be raising your hand towards him, ALL BEFORE YOU DO ANY OF THESE THINGS!
It's all about the fact that he doesn't yet know you, let alone trust you...And what do we as people do when we are approached by someone that we don't really know well and who we certainly don't trust? How would you react if you were in the grocery store and a person that you don't know well at all and that you don't trust simply walked over to you, without hardly saying a word except maybe "Hi" or "Good Morning", and then they got right up near you, and then reached their hand out towards your body and put it right in your face? Maybe a little "apprehensive"...
