Digital rank of noise lies within unwritten limits (7)
I believe the answer is:
ordinal
'digital' is the definition.
(thesaurus)
'rank of noise lies within unwritten limits' is the wordplay.
'rank of noise lies' becomes 'd' (I can't justify this - if you can you should believe this answer much more).
'within' becomes 'in'.
'unwritten' becomes 'oral' (synonyms).
'limits' is an insertion indicator (limit can mean to contain or block off).
'd'+'in'='din'
'din' placed inside 'oral' is 'ORDINAL'.
Can you help me to learn more?
(Other definitions for ordinal that I've seen before include "For example, first" , "Number in a sequence" , "Possibly first or second" , "Maybe first" , "Roman Catholic service book" .)