Rex takes snake out of grating (4)
I believe the answer is:
rasp
'grating' is the definition.
(thesaurus)
'rex takes snake' is the wordplay.
'rex' becomes 'r' (common abbreviation e.g. GR=George Rex, King Georg).
'takes' is a charade indicator (letters next to each other).
'snake' becomes 'asp' (asp is a kind of snake).
'r'+'asp'='RASP'
'out of' is the link.
(Other definitions for rasp that I've seen before include "Harsh noise - file" , "Filing tool" , "unpleasant noise" , "Smoother" , "Grate; scrape" .)