2016 Cadillac ATS- Radio does not wait for a Cue

Have 2016 Cadillac ATS. On several occasions, when starting the car, the radio comes on automatically. Been to the dealer 3 times, they don’t know what is causing this to happen. Has anyone else experienced this problem??

I assume the audio system is off when you shut the car off, right?

Is the audio system turning on to one of the radio bands (AM or FM) or to something else like the Bluetooth input?

yes the car is shut off and before doing that=the radio is also shut off—comes on to the last station played most often sirius station