Dear Jeanne,
Your son's behavior is not typical of children his age, and probably does not fall within the boundaries of normal spectrum childhood behavioral difficulties.
It would be prudent to seek evaluation by either a child mental health professional or a developmental pediatrician (or team). What I have in mind is the possibility that your son displays a type of childhood emotional condition called Pervasive Developmental Disorder. Some of his behaviors certainly typify this category of illness.
I would look into one of the many kinds of autism. autism.com and feat.com are two good sites for you to learn. Also read "Special Diets for Special Kids" by Lisa Lewis.
I know this is hard to consider, but do you have any knowledge of autistic spectrum disorders or PDD-NOS? You might be dealing with any number of things that are not autistic spectrum. I hop you will visit my web page. My son was not developing language until a little after 3. Then it was mostly just naming things. Communcation started by reciting lines from videos and books.
He has semantic-pragmatic disorder and central auditory processing disorder, possibloy developmental dyspraxia. Some think SPD is autistic spectrum, but I don't agree. But in my research I have had the opportunity to read information on this, and screeching tends to be one symptom. Please don't be afraid to explore this. You can help your son so much by knowing. I know what it feels like to consider that your darling has a problem, but it is better for him to face this head on. The sooner any issues are addressed the sooner he can reach for his potential. Please feel free to visit my web page at:
www.geocities.com/denisev2/