Sound of the engine when you turn up with a posh car (4)
I believe the answer is:
purr
'sound' is the definition.
(I know that purr is a more specific form of the action resonate)
'turn up with a posh car' is the wordplay.
'turn' is a reversal indicator.
'with' means one lot of letters go next to another.
'a posh car' becomes 'rr' (short for Rolls Royce).
'up' in reverse letter order is 'pu'.
'pu'+'rr'='PURR'
'of the engine when you' is the link.
I am not very happy about this link. Some or all of it may belong to another bit of the clue.
Can you help me to learn more?
(Other definitions for purr that I've seen before include "Sound like happy cat" , "Low vibratory sound" , "Sound of happy animal" , "Cat's contented sound" , "4's sound" .)