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' indicates putting letters inside.
'strange' is an anagram indicator.
'note' with letters rearranged gives 'tone'.
'ss' going around '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" .)