My first thought is, that couldn't be the cause, as I left all the connections as they were (didn't break down after the show, did not disconnect 5 pin from Nbox). The whole assembly remained intact, then I tried to reproduce the problem at home. If the clicking occurred while recording in the venue, then couldn't be duplicated later, with nothing being disconnected or tampered with in the meantime, then how would a loose connection have suddenly gotten tighter (especially with the "lock-down" construction of this particular unit)?
However, on second thought, when I tried to reproduce it at home, it wasn't the same SPLs as in the venue. There does definitely seem to be a correlation between the clicking and the input level. So perhaps you are right.