Forced pep felt wrong, making sound change (7,6)
I believe the answer is:
doppler effect
'sound change' is the definition.
The definition and answer can be both types of natural phenomena as well as being singular nouns.
Maybe they are linked in a way I don't understand?
'forced pep felt wrong' is the wordplay.
'wrong' indicates anagramming the letters.
'forced'+'pep'+'felt'='forcedpepfelt'
'forcedpepfelt' with letters rearranged gives 'DOPPLER EFFECT'.
'making' is the link.
Can you help me to learn more?
(Other definitions for doppler effect that I've seen before include "Sonic phenomenon" , "Phenomenon explaining the change of pitch of a passing siren" , "Apparent drop in pitch of passing sound" .)