Lift starts to rattle after initially smooth elevation (5)
I believe the answer is:
raise
'lift' is the definition.
(I know that lift can be written as raise)
'starts to rattle after initially smooth elevation' is the wordplay.
'starts to' indicates taking the first letters.
The first letters of 'rattle after initially smooth elevation' is 'RAISE'.
(Other definitions for raise that I've seen before include "Advance" , "Cultivate by growing" , "Uplift" , "Lift, elevate" , "Bring up, rear" .)