I am having the issue described as well and am curious about how widespread it is. So far in this thread two users report experiencing it, while one says that a replacement device does not exhibit the same behaviour. Adding myself into the mix that makes it 3-to-1 noticing the slight brief buzz at the beginning of the vibration, when set to the highest intensity. It's an even bigger issue when using a multiple quick-repeating vibration, as the little rattle/buzz sound will happen at the beginning of each individual pulse. A small issue maybe, but an irritating one.
Can anyone else confirm either definitely having, or not having this issue?
To test it, it's easiest to go to Vibration Intensity under settings, and flip the slider back and forth between the highest, and second highest levels, to see if you notice a difference. In my case, it sometimes won't happen depending on how/tightly I'm gripping the phone. Most often it will though.