I also received an ST16 with a part rattling around inside. I opened the case, only enough to shake out the detached cooling fan motor blade/rotor. I was unable to completely open the case. As of now, Yuneec has NOT responded to my inquiry asking for directions on what to do.
I have flown the 'H' several times with no ill effect but the outside air temperature has been moderate - below 90 F.
Don't know if this will work but this post shows the st16 apart, also others discussing the loose fan items. Hope this helps?
Its post #17 in this discussion..