Car is a '16 GTS so now 7-8 yrs old. Normal procedure-start engine turn radio off, A/C off windows part way down and drive. About 3-4 months ago noticed that radio will all of a sudden start playing without any reason requiring a second manual 'shut off'. No other electronic issues or problems except it can be a little startling when it occurs especially if the volume is up. First thought was battery which is the original but it checks out at 100% plus capacity on multiple occasions and I keep it on a tender. Thoughts?

 

Could be the battery starting to show signs of its age. It’s approaching or at 8 years old already.

 

I keep wondering that. That is why I keep testing but it checks out ok