Stereo volume increases on its own

While I haven't seen this issue on your vehicle, it does happen and the normal cause is the volume nob on the radio or the steering wheel control has some dirt/grime/food in it and causes it to stick and the volume will go on its own. The only way to correct it is to replace the switch or radio. I would suggest replacing whichever you use more. For me I rarely use the actual radio knob so I would replace the steering wheel switch first.