J.C.
D.,
Both of my daughter's have done this. Although my oldest has only started since her sister does it. My girls are 25 months and 12 months. They do it back and forth like they are talking to each other but it is very annoying and it is usually when they are done and getting bored. What I have started doing is cleaning up my oldest daughter and letting her go play in the living room while I finish cleaning up dinner and get ready for bath time. It does seem to work.
Hope the shrieking ends soon for you!
Good luck!
J.