Stack Beano at first with earlier back issue (7)
I believe the answer is:
lumbago
'back issue' is the definition.
(muscle pain in the back)
'stack beano at first with earlier' is the wordplay.
'stack' becomes 'lum' (both can mean a chimney).
'at first' suggests taking the first letters.
'with' is a charade indicator (letters next to each other).
'earlier' becomes 'ago' (I've seen this before).
The first letter of 'beano' is 'b'.
'lum'+'b'+'ago'='LUMBAGO'
(Other definitions for lumbago that I've seen before include "Gaul mob (anag.)" , "Rheumatic pain in muscles of lower back" , "Back affliction" , "Form of backache" , "Rheumatic pain in the small of the back" .)