loma:
Screaming passengers in the back? - possibly
A cabin call ? - possibly
A radio call ? - less likely
An engine temp indicator? - unlikely
ADD - Groundcrew running away.
The biggest hazard is, as you have highlighted, inexperienced c/crew initiating an evacuation or pax panicking. Another one rarely seen (by me anyway) these days is the 'wet start' with clouds of smoke.