When starting the NATO Showcase mission on your right you have all types of HEMTT parked there. When you stand at the quadbike at your left and look towards the HEMTT Ammo truck it will suddenly appear as though its lights are burning + something seems to be lifted up at the topback of the cabin area.
When walking towards the HEMTT Ammo from this position the lights go back out + the lifted 'thing' disappears. It seems the distance from your person to the HEMTT Ammo truck changes this visual behaviour. {F22929}