Still, it is interference (6)
I believe the answer is:
static
I believe this clue is a double definition.
'still' is the first definition.
('static' can be a synonym of 'still')
'interference' is the second definition.
(static is a kind of interference)
'it is' is the link.
(Other definitions for static that I've seen before include "Its cat (anag)" , "Inert, motionless" , "Crackling or hissing noise caused by electrical interference" , "Inert or passive, like some electricity" , "irritation for the listener?" .)