Hi MandeeMoo,
It is quite normal for some babies the age of yours to make loud shrieking sounds, allbeit annoying to the sensitive ears of older people. Try and take your son to another room, for a walk or a ride when he is actively alert and playful. You have a higher tolerance because you are his mom, you are young and it is no big deal to you.
Due to the fact you are living with your grandparents, take into consideration that their ears are vunlerable to shrieking sounds as that of your baby squealing. Be a little more sensitive to their uncomfortableness and tell them you are sorry for your sons high pitch sounds and you will do what I outlined above when he is very active and playful. Do something really speacial for your grandparents for allowing you and the baby to live with them. Cook a nice meal, make a quilt, take them to a movie, say Thank You, go out of your way and do little extra things around the house, like vaccuming, ironing, cooking, cleaning...something to show them you appreciate and love them.
God Bless,
Faded Rose