No, there has never been any force trim in any 206 model. I've flown pretty much all of them, from the OH-58, B2 & B3, and all the L models from the straight L on. No force trim, just cyclic friction.
I also think it's the pax moving around. They don't have to release their seat belts, just lean quickly. I've had a full load of pax start moving in unison, just to mess with me, and it can start lots of movement. I would just amplify the movement, and they would soon stop.