Snake in the grass half-heartedly made sound between a hiss and a rattle (6)
I believe the answer is:
rasped
'sound between a hiss and a rattle' is the definition.
I can't judge whether this definition defines the answer.
'snake in the grass half-heartedly' is the wordplay.
'snake' becomes 'asp' (asp is a kind of snake).
'in the' means one lot of letters goes inside another.
'grass half-heartedly' becomes 'red' (I can't explain this - if you can you should believe this answer much more).
'asp' inserted inside 'red' is 'RASPED'.
'made' is the link.
Can you help me to learn more?
(Other definitions for rasped that I've seen before include "Of voice, made a rough grating sound" , "Uttered in a grating voice" , "Made harsh grating noise" .)