Sound in new GMC kicks down, is it my iPhone?

We have a new 2024 GMC Sierra. I noticed that from time to time, the volume on the radio (am/fm/satellite) kicks down unexpectedly, then returns to the preset volume within 15-30 seconds. We took it to the dealer, but they could not replicate (of course!). As I am driving home, the volume kicks down, so I grab my iPhone (that is on the GMC wifi and is paired to the system) and try to get the return of the volume to normal on video. Accomplished, but as soon as I stop recording video, the volume dips again. I tried this in the driveway, and every time I start or stop video recording, the volume dips for a few seconds. I was not touching my iPhone when the volume dipped to begin with, but I have to wonder if it is something my iPhone 13 is doing? I don’t want to power off my phone to listen to Sirius on a long drive (we had a 6 hour drive and the constant fluctuation in volume was very annoying). Any help is appreciated!