Not sure about headlights. Def gone with AC. I forgot if it goes away with just the climate control fan only.Do your vibrations continue with the headlights on? For me I just have turn something on that uses a moderate amount of power such as headlights or the fan and the vibrations go away. Im sure the defrost, which requires a lot of power will do the same for me.
In fact, with my headlights on I dont see a drop/rise in the tach when I shift between neutral and drive. When all the accessories are off though I can see the tach move when I shift between neutral and drive.