There is a arm with a pivot in the middle much like a see saw when you were a kid. One end of this moves a plunger up and down on the smoke unit. The other end of this arm moves up and down between a sensor. In my case the arm wasn't going down far enough to activate the sensor. I bent the end of the arm just a wee bit so it would activate the sensor and hence the chuff sound.
I presume you used a pair of needle nosed pliers to bend the arm. Did you bend it right at the see/saw joint? That's where I'm trying it and it just doesn't want to seem to bend and I don't want to break it.