Help for DS who screams in frustration

[csa12]

I am at my wits end. DS is 27 months and screams a blood curdling scream when he is frustrated with his toys. He also screams when strangers say hi to him or sometimes when other children play in the same area he is playing in. I am a believer in the philosophy of positive discipline and I am trying to teach him to say "hello" and "need help" and that "screaming hurts mommy's ears", but I nearly lost it today when he screamed at another little girl and her grandmother told me "can't you tell him to stop!". I know I may be projecting onto DS and that I shouldn't let other people's reactions bother me, but I really want to know what else I can do to stop this behavior. DH is very mild mannered and never yells, although I admittedly do raise my voice, but since recognizing that DS picks up on this, I have toned it down considerably. I know, I know he most likely picked it up from me, but I am trying my best to rectify the situation!

Thanks for any help,
Cheryl