I'm late to this post but I've had similar problems and I am concerned about two things. One is the tire pressure (as already mentioned) and the other is that I suspect the tires are being used mostly in SOCAL temps and only some times in snow. If this is true, it may affect the sidewall as well. I think that was partly what did my in. If I am repeating a comment, forgive me, haha.
 
Mike