The most common and most likely answer to this crossword clue is the 4 letter word YAPS
Y
A
P
S
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The straight part
We know that "shrill sounds" is the straight/definition part of the clue. The straight part is often a synonym or definition, in this case shrill sounds = yaps.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 YAPS mean?
YAPS noun- The high-pitched bark of a small dog, or similar.
- Casual talk; chatter.
- The mouth, which produces speech.
- A badly behaved child; a brat.
- Of a small dog, to bark.
- To talk, especially excessively; to chatter.
- To rob or steal from (someone).