Rumbling sound coming from first of teenagers, hot, below (7)
I believe the answer is:
thunder
'rumbling sound' is the definition.
(I've seen this before)
'first of teenagers hot below' is the wordplay.
'first of teenagers' becomes 't' (1st letter of 'teenagers').
'hot' becomes 'h' (abbreviation, eg on taps).
'below' becomes 'under' (synonyms).
't'+'h'+'under'='THUNDER'
'coming from' acts as a link.
(Other definitions for thunder that I've seen before include "Hunt red (anag)" , "Hurt Ned (anag) - loud noise" , "Rumble after lightning" , "Move fast, noisily, and heavily" , "Booming noise after lightning" .)