You are making some progress with Felix but the noise is a complaining noise. Callisto, my 'tiel, makes the same noise. It basically means stop and leave me alone because you are irritating me and I am getting upset. The good thing is he is not trying to bite you but you have to consider that when you reward him while he is making that noise he may start to associate the reward (something positive) with the noise and continue doing that. When I work with Callisto she will make the noise, then stop for a bit and I will give her some scratches and then she will start again. I usually just put her back in her cage. I don't know if she always made the noise or if, in her case, it is related to her bad foot and she doesn't want me touching it or she is afraid I am going to give her something she doesn't want or like. She was at the vet for a while after she was brought in by the person who found her and she was treated for her foot injury and whatever else may have been going on.