Rattlesnake in the Front Yard

There I was, exiting the house with Jack for an evening walk, Jack walks right by the above.  Having received snake avoidance training, I was surprised there was no reaction but apparently, it's the sound of the rattle that kicks in the training and sure enough, once the snake initiated the rattle, Jack freaked out, so that's good.  What provoked the snake to rattle???

I alerted Amy that we had an unwanted visitor, grabbed a bucket and broom and coaxed the snake (I was surprised this worked) into the bucket.  The bucket handle was well within strike range so I placed the broom firmly on the snake and walked about 100 yards where we released it into the wild.  It was one pissed off snake when I shoved the bucket over and it slithered out.