Empty trash below and rumble threateningly (7)

I believe the answer is:

thunder

I'm a little stuck... Click here to teach me more about this clue!

'rumble threateningly' is the definition.
'thunder' can be an answer for 'rumble' (I've seen this before). I am not sure about the 'threateningly' bit.

'empty trash below' is the wordplay.
'empty' says to hollow out the word (remove centre letters).
'below' becomes 'under' (synonyms).
'trash' with its centre taken out is 'th'.
'th'+'under'='THUNDER'

'and' acts as a link.

Can you help me to learn more?

(Other definitions for thunder that I've seen before include "Loud and prolonged noise in the sky" , "Hunt red (anag)" , "Rumble after lightning" , "Move fast, noisily, and heavily" , "Hurt Ned (anag) - loud noise" .)

I've seen this clue in the Sydney Morning Herald.

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