Find out about the noise (6)
I believe the answer is:
rumble
I believe this is a double definition.
'find out about' is the first definition.
(I've seen this before)
'the noise' is the second definition.
(rumble is a kind of noise)
(Other definitions for rumble that I've seen before include "Carriage seat gives the sound of heavy wheels" , "street-fight between gangs" , "Discover the truth about" , "Discover (illicit activity); continuous deep noise" , "Low, vibrating (traffic) noise" .)