My Cat makes an unusual noise

We recently adopted a kitten from a local shelter who had supposedly been born to a feral mother. They believed her to be 3 -4 months old however after our vet examined her he thinks she is more likely about 6 mos even despite her very small size.
   
I have had many cats throughout my life but there is something different about Cleo. Firstly she has taken to one of my children so much so that she rarely leaves his side, and if one of the other children and him are arguing she backs against him almost like she is going to defend him. I have just never had a cat behave that way before. She is very loving with all of us but particularly protective of him.
   
The other thing odd is a sound she makes. She meows like an ordinary cat but she also makes another noise I have never heard a cat make before. Its not purring, its not meowing its sounds like a "gurgling dove", she almost sings a little song, usually when my son comes in from school and she goes straight to him.
   
I was just wondering if there is a particular breed this "Sound" and temperment may be attributed to.
   

Cleo apparently has a strong maternal instinct & has chosen your son as the object of her care. Some cats do this. I've heard of this, but never actually seen it.
   
This is great for your son, he now has a cat all his own who really, really cares for him. He won't be alone for the next 12 or more years.
   
And yes, she just may defend him with all of her weapons if she thinks he's really in danger - at least until she decides that he's big enough to defend himself; then she'll settle down & relax. Make sure the other kids realize this, so she doesn't do damage to them if she feels it necessary to actively defend your son.
   
At least she loves everybody else, too - she just realizes that other Young Animals (the other kids) do get out of control & she may have to deal with them.
   
Cleo may have grown up a lot faster than other cats; she probably considers herself an adult.
   
As to the voice: What does Cleo look like? Does she have big triangular ears, a somewhat pointed face (but not exaggerated like a Siamese cat), long legs, thin-ish body, and possibly tiger-striped or with coloring like the link below?
   
Does Cleo, by any chance, sound a little like R2D2 (the little robot from Star Wars)? Kind of musical? Making musical sounds in her throat that resemble birdsong, tweets, "Purrrrr-up!" sounds, almost mechanical sounds, that kind of thing?
   
If so, you may very well have yourself a part-Abyssinian cat (called Somali cats if their fur is a little long).
   
In fact, the more I think of it, the more it could be likely.
   
Abys are dog-like in their devotion to their people. They frequently attach themselves to one person in the house more than the rest, but truly love people in general.
   
They're very talkative (like Siamese), but have very musical voices (unlike Siamese).
   
They talk A LOT. To their people. To themselves. When they're walking down the hall or rummaging in the closet.
   
(Ah, I remember Fred, my half-Aby, mucking about in the closet making happy little sounds to himself as he discovered things he'd forgotten were in there. I swear, I heard question marks on the end of some of his sounds.)
   
They will meet you at the door, greeting you with all the news of the day.
   
They're incredibly smart. They can be trained to walk on a leash. Some of them teach themselves to fetch their balls & skin mice, so their people can throw them down the hall to chase (my Fred did.)
   
They figure out how to get into things (better make sure the pretty shiny things that look like cat toys are safely out of the way; pay attention to the gaps to be jumped; Abys are particularly skilled at jumping up high & across wide spaces).
   
They're incredibly elegant-looking; many of them strike a pose when they sit on the arm of the couch.
   
An Aby is classified as a Tabby Cat. Although the purebred's coloring looks even, actually each of the hairs on their bodies are striped. When a purebred Aby or Somali is crossed with any other breed of cat, the offspring frequently come out as tiger cats (Tabby cats). The striping, when watered down with the other breed, changes format.
   
They're one of the finest cats to have in a family, I love them.
   
So, did I help any?
   
View External Link

She does sound like R2D2!
   
I don't know about the rest she is partially striped and her eyes are maybe more slanty than other cats I have had and they are light green. I think most of the other cats we have had had gold eyes.
   
Here is a picture of her. its the one from the shelter's website and not very good. She actually looks kind of big in the picture but she weighs just barely over 3lbs.
   
My son actually named her Cleopatra because he thought she looked like she was wearing eyeliner. I thought that a bit of a mouthfull for our youngest child (She is 19mos) so we shortened it to Cleo....