Heard beer was trouble (3)
I believe the answer is:
ail
'trouble' is the definition.
(I know that trouble can be written as ail)
'heard beer' is the wordplay.
'heard' shows a homophone (sound like).
'beer' becomes 'ale' (type of beer).
'ale' sounds like 'AIL'.
'was' is the link.
(Other definitions for ail that I've seen before include "Become sick" , "Trouble, afflict; be sickly" , "Cause to feel indisposed" , "upset" , "pain" .)