Rocks ship with strange note (6)
I believe the answer is:
stones
'rocks' is the definition.
('stone' can be a synonym of 'rock')
'ship with strange note' is the wordplay.
'ship' becomes 'ss' (prefix in ship names eg SS Great Britain).
'with' is an insertion indicator.
'strange' is an anagram indicator.
'note' with letters rearranged gives 'tone'.
'ss' enclosing 'tone' is 'STONES'.
(Other definitions for stones that I've seen before include "Small pieces of rock" , "Pebbles" , "Gems -- Mick Jagger's rollers?" , "Balls" , "lots of rock" .)