The most common and most likely answer to this crossword clue is the 9 letter word SUBWOOFER
I've seen this crossword clue in The Guardian
S
U
B
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More clues leading to the result SUBWOOFER
- Lend setter, for example, audio equipment
- Sound of setter filling puzzle up for speaker
- Low-pitched noise from this replacement dog
- Part of a loudspeaker, the underdog?
- A sound driver, this underdog?
- Court judge upset supporting deputy speaker
- Speaker woe for us, unfortunately — keeping Bercow initially
- Very low speaker to make an advance to solicitor holding bit of freehold
- This underdog makes a lot of noise
- Speaker may be underdog
Buddy explains!

The straight part
We know that "Low-pitched noise from this" is the straight/definition part of the clue. The straight part is often a synonym or definition, in this case low-pitched noise from this = subwoofer.The cryptic/wordplay part
In cryptic crossword there's often an wordplay/cryptic part as well.This part involves a more complex hint, such as an anagram, homophone, hidden word, etc.
Sadly, We don't have an explanation for this specific crossword clue yet.
What does SUBWOOFER mean?
SUBWOOFER noun- An electronic speaker designed to produce low-frequency sound, especially bass.