Address system in centre certain to cause bother (6)
I believe the answer is:
tannoy
'address system' is the definition.
(public address system)
'centre certain to cause bother' is the wordplay.
'centre' indicates the central letters.
'to cause bother' becomes 'annoy' (to annoy someone is to cause them bother).
The centre of 'certain' is 't'.
't'+'annoy'='TANNOY'
'in' is the link.
(Other definitions for tannoy that I've seen before include "Public address system" , "Speaker" , "Loudspeaker system" , "Public-address system" , "Orator's amplifier" .)