In my heathen youth, when I was living on a commune, a… um.. Rainbow Gathering type fellow came to visit. He brought mushrooms and a knapsack full of Aztec death whistles. He went on and on about the horrifying, mind-altering sound they made, like a captured death-scream, and about their many healing and vision-inducing qualities. Wow, all that in the same simple clay skull whistle? Did I mention he had mushrooms?
A group of us took the 'shrooms and joined him for a death whistlepalooza. The mushrooms were mild and the claims of panic-inducing fear at the sounds of the whistles even weaker.
Don't get me wrong, I admired the whistles, and there is plenty of evidence that Mesoamerican cultures had an extremely sophisticated understanding of acoustics and acoustical engineering. But, in the end, I found the sound creepy and shrill but nothing extraordinary. I can certainly imagine them being unnerving to hear at a human sacrifice or hundreds sounding on a battlefield.