Turned up by car - you can just hear the engine (4)
I believe the answer is:
purr
'can just hear the engine' is the definition.
I can't judge whether this definition defines the answer.
'turned up by car' is the wordplay.
'turned' says the letters should be written backwards.
'by' says to put letters next to each other.
'car' becomes 'rr' (Rolls Royce).
'up' reversed gives 'pu'.
'pu'+'rr'='PURR'
'you' is the link.
Can you help me to learn more?
(Other definitions for purr that I've seen before include "Show pleasure" , "Sound of happy animal" , "Sound like happy cat" , "Tiddles' sound" , "Noise of a contented feline" .)