iPhone 12 Pro max volume increases to max

New iPhone 12 Pro max ... volume control when playing back videos of any kind just slowly creeps up to max within about 5 - 8 seconds. Did a restart, reset and restore ... problem resolved for a few days after restore, but is back again now. Even once the video is finished, I have watched the volume slowly creep up without anything playing or me even touching the phone. Seems it may be hardware related? Not sure.