The only pressure cooker I've ever owned (against my better judgement) did indeed start to hiss and then whistle alarmingly when it was ready to be taken off the heat.
I don't currently own one, but I remember my mother using hers fairly frequently. It had a small vent hole to release pressure, upon which sat a very heavy metal knob that acted as the pressure regulator. It sat loosely on a small tube, and when the pressure built up enough to lift the heavy weight, a small amount of steam could escape from underneath it.
Thus once the cooker got to pressure, it constantly hissed and made little tinging sounds as the weight lifted and settled. I can't remember if it made a whistle when done or not, but I actually kind of enjoyed that hissing and putt-putt-putting sound. It was almost like listening to a steam engine.
However, one time I made the mistake of adding whole rosemary to whatever it was we were cooking. One of the individual little leaves somehow managed to get carried up into the steam release vent, so pressure kept building instead of seeping off.
All of a sudden there was a very loud bang as what had essentially become a bomb on the stove blew some seals and spewed hot liquid all over the kitchen ceiling and immediate area. In the aftermath, we found a small rubber gasket or o-ring that had blown out of the lid where that pressure relief tube sat in the lid, with a piece of rosemary in it. I presume that was an intentional design feature so that instead of the entire pot exploding in metal shards like a grenade, this gasket failed first.
It did however send that pressure relief weight high enough to dent the ceiling. I discovered this as I was on a step ladder trying to clean the red stains (apparently we were cooking something tomato based) off the ceiling. Eventually we just had to repaint the ceiling.
As a result, to this day my mother still refuses to use a pressure cooker, and views rosemary with scorn.