It does tend to happen when accelerating .. however I believe the rattle sound is caused when the wastegate acuator rod vibrates so any movement in that area can potentially cause it to make the tinny sound. The clip basically mutes it.

So you can picture it - https://www.google.com.au/search?q=w...DMMyaPXufjM%3A

Can't recall if mine made the noise when off the throttle though, sorry.