Part of organ Sheeran featured in strange poster (4,4)
I believe the answer is:
reed stop
'part of organ' is the definition.
(I've seen this before)
'sheeran featured in strange poster' is the wordplay.
'sheeran' becomes 'ed' (Ed Sheeran).
'featured in' indicates putting letters inside.
'strange' indicates anagramming the letters.
'poster' with letters rearranged gives 'restop'.
'ed' inserted into 'restop' is 'REED-STOP'.
(Other definitions for reed stop that I've seen before include "Set of organ pipes; do preset (anag.)" , "part of organ" .)