The most common and most likely answer to this crossword clue is the 6 plus 8 letter word CANNED LAUGHTER
I've seen this crossword clue in The Times
C
A
N
N
E
D
L
A
U
G
H
T
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R
More clues leading to the result CANNED LAUGHTER
Buddy explains!
The straight part
We know that "What's coming off a track as a result of cracks?" is the straight/definition part of the clue. The straight part is often a synonym or definition, in this case what's coming off a track as a result of cracks? = canned laughter.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.