Might be inside the vehicle but it happens when it's cold and wet out, now mind ya, mine stopped doing it and it was only a handful of times throughout the winter. If I recall correctly I was also getting a Check E-brake notice or ABS, I do believe it was that, might be off ... two errors on starting the LS, turning it off and restarting always made it go away. Just putting it in reverse and backing out made it go away as well. It was mostly during the extreme cold snaps.
I could care less, it went away, I have one of those self correcting models it would seem. If it acts up again, I'll trace it down but something tells me something underneath is not liking the wet/damp conditions throughout the winters. It's not doing it in the rain, so it's related to cold temps, something freezing up, dampness shorting something related to the wheels.