Explode: instrument going up, by the sound of it? (5)
I believe the answer is:
rebut
'explode instrument' is the definition.
'rebut' can be an answer for 'explode' (both can mean to debunk something false). I'm not sure about the 'instrument' bit.
'going up by the sound of it?' is the wordplay.
'going up' is a reversal indicator.
'by' says to put letters next to each other.
'the sound of' becomes 'uber' (I am not sure about this - if you are sure you should believe this answer much more).
'uber' put after 't' is 'tuber'.
'tuber' in reverse letter order is 'REBUT'.
(Other definitions for rebut that I've seen before include "Drive back" , "Contradict or disprove" , "Deny claim" , "Scotch" , "Overthrow by argument or proof" .)