Old rulers' just interjections voiced (8)
I believe the answer is:
pharaohs
'old rulers'' is the definition.
(rulers of ancient Egypt)
'just interjections voiced' is the wordplay.
I cannot quite understand how this works, but
'interjections' could be 'ohs' (I've seen this in another clue) and 'ohs' is located in the answer.
This explanation may well be incorrect...
(Other definitions for pharaohs that I've seen before include "Royal rulers of ancient Egypt" , "Ancient Egyptian kings" , "Ancient Egyptian royalty" , "Ancient kings of Egypt" .)