Sequence of electric and gas operation in water heater

I almost always run my Surburban on both electric and gas at the same time for fast recovery when taking showers.
Don't know what my thermostats are set for but the gas almost never turns on unless we are using hot water for showers or clothes washer.
If the electric is not on, then I often hear the gas kick on to reheat the water, especially if the weather is cool. Annoying at night.