Some metallic sounds when reflected vary in frequency (9)
I believe the answer is:
oscillate
'vary in frequency' is the definition.
'oscillate' can be an answer for 'vary' (thesaurus). I am unsure of the 'in frequency' bit.
'some metallic sounds when reflected' is the wordplay.
'some' indicates the answer is hidden within the clue (some of the parts of the word are used).
'reflected' is a reversal indicator.
'etallicso' is hidden within 'metallic sounds when'.
'etallicso' written backwards gives 'OSCILLATE'.
Can you help me to learn more?
(Other definitions for oscillate that I've seen before include "Waver between various options" , "Swing to and fro with lost Alice" , "sway" , "shake" , "Swing back and forth" .)