The tension shows in the music (6)
I believe the answer is:
strain
This clue could be a double definition.
'the tension' is the first definition.
('strain' can be a synonym of 'tension')
'shows in the music' is the second definition.
'strain' can be an answer for 'music' (strain is a kind of music). I'm not certain of the 'shows in the' bit.
Can you help me to learn more?
(Other definitions for strain that I've seen before include "Noted" , "Weaken -- sieve" , "Blood" , "Injure (a muscle); distinct breed" , "Drain off" .)