The most common and most likely answer to this crossword clue is the 4 letter word WHIR
I've seen this crossword clue in The Guardian
W
H
I
R
Buddy explains!

The straight part
We know that "Buzzing/Buzzing" is the straight/definition part of the clue. The straight part is often a synonym or definition, in this case buzzing/buzzing = whir.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 WHIR mean?
WHIR noun- A sibilant buzz or vibration; the sound of something in rapid motion.
- A bustle of noise and excitement.
- To move or vibrate (something) with a buzzing sound.
- To make a sibilant buzzing or droning sound.
- To cause (something) to make such a sound.