Went through this a while ago. She was just learning about her vocal chords, and how loud she can go. Irritating as it may be, I took the opportunity to train my patience and tune it out, or respond patiently and softly so she learns that:
- she need not scream to get my attention
- screaming does not beget screaming, it is not "normal" to reply with a scream
- when mama wishes for her to tone down, mama is pleased when she does (positive reinforcement when she stops screaming)
My MIL used to scream or echo louder after bubbles' scream to drown out or startle her, which only resulted in a screaming match. I spoke with MIL countless times and demonstrated to her that bubbles will tone down if we respond in kind. She is only learning about her pitch and volume capabilities. It is a developmental phase.
For bubbles, she screamed and squealed for a few alternating days lasting a week. Till today, when she sees my MIL she tends to scream, but thats cos MIL communicates with her with odd shouting baby-talk, so truly, it is monkey see, monkey do, as she doesn't do it with me, or her father.