how common is it for a gun to just fire at a random time ?
Well, it's very common, and usually when it happens the gun erupts in fully-automatic mode.
That SUV reference was interesting. It reminded me of thirty years or so ago when any reference on TV news to a handgun always called the weapon a "Saturday Night Special".
Then the news started calling hollow-points "dum-dum" bullets, a term I'd never heard before the press started using it.
Then of course we had the notorious "cop killer" bullets, and the undetectable plastic Glock pistols.
And now we're under siege by assault weapons since repukes repealed the lifesaving "Assault Weapon Ban" that the Hildebeast vows to reinstate.