Is among a tray of something grammatical? I am not sure but using among before a singular word seems ungrammatical, but I am not sure, because it's a tray of a bunch of things.
I found this particular excerpt, but I am not sure how grammatical it is. Many of the results from Google use archaic language or just straight out incorrect language.
...a main document selector designed to select a desired document from among a tray of encoded documents transported thereto...
A toy was hidden among a tray of other toys