How do I quiet my 16 mo. old daughter's constant yelling without losing my mind?

My 16 mo. old rarely talks. . .she yells everything. I have tried to determine if it's cuz I yell excessively. . .it's not. . .She literally runs around the house yelling and hollering, not so much squealing, just yelling. She is the loudest kid I've ever heard. Her 3 yr. old sister even covers her ears in frustration sometimes. My 16 mo. old thinks the yelling is funny, I don't want to "yell at her" for yelling, or her for something so meanial. . but meanial as it is it's making my husband and I crazy. . it's been going on for months! Any ideas. . .we ask her to be quiet, we shush her, we startle her into paying attention to what we're saying, this combined with the sudden need to be attached to my hip or she screams bloody murder is testing my patience. She was always very independent and has only in the last few months started needing to see me every waking second or she cries like its the end of the world.. . Does she need a doctor? Some thoughts'd be great b4 I do.