Dissimilar materials scraping or rubbing against one another will cause a transfer and build up of static charge, often leading to a discharge event. This transfer is called tribocharging.
Long ago, fuel tanker trucks had a steel chain that they dragged along the roadway. The idea was to provide a continuous discharge of static electricity to the earth via the chain and prevent a big spark and an explosion. Static would build up on the tanker truck body just because rubber tires were rubbing the road. The chains disappeared when all tires were made to be slightly conductive (excess carbon), so as to thwart tribocharging.
Another source of static radio noise from gas powered vehicles comes from spark plugs and the wires that connect to them. When car radios first appeared, they were almost useless because of spark plugs and their noise. This problem was solved by making spark plugs wires fairly resistive. That softened the sharp crack of the spark and mitigated the noise. Not all engines are so equipped, however. I can't use my portable lightning detector on my boat, for example, because my Merc outboard makes too much noise.
My portable lightning detector works fine on my car, though...except when the automatic transmission changes gears. That's when an electric solenoid is activated, making a sharp crack that can be picked up a couple of car lengths away.
So there are many ways a vehicle might trip up a lightning detector. BTW, the frequency that the AMS chip listens on is 0.5 MHz, or 500 KHz.
