We have a 6 and 6+ and when we first heard the vibrator rumble, we knew it sounded off. It makes a buzz noise and the vibration is noticeably weaker. My question is, is mine defective? From a quick google, it seems to vary between 6+'s and some posters are saying that a replacement solved the problem. The fact that no one here cares about silent mode tells me mine is a rare case but I want to be certain that it is a problem.