Radio noise (6)
I believe the answer is:
static
'radio noise' is the definition.
(I've seen this in another clue)
This is the entire clue.
(Other definitions for static that I've seen before include "Still, unchanging" , "Cast it (anag) - unmoving" , "Constant interference" , "Not moving - electrical interference" , "Inert, motionless" .)