Some said it to be a problem (3)
I believe the answer is:
sum
'problem' is the definition.
(arithmetic problem)
'some said' is the wordplay.
'said' indicates a 'sounds like' (homophone) clue.
'some' is a homophone of 'SUM'.
'it to be a' acts as a link.
I am not very happy about this link. Some or all of it may be part of another bit of the clue.
Can you help me to learn more?
(Other definitions for sum that I've seen before include "Arithmetic calculation" , "An additional problem" , "Mathematical problem" , "See 25" , "Aggregate, total" .)