The most common and most likely answer to this crossword clue is the 10 letter word RATTLETRAP
I've seen this crossword clue in The Daily Telegraph
R
A
T
T
L
E
T
R
A
P
More clues leading to the result RATTLETRAP
- Some rejected behind conductor in rickety bus?
- Rickety vehicle upset some when reversing
- Vermin on platter chewed banger
- Knackered old bus conductor’s role reversal
- Conductor has to catch rickety old bus
- Distress character reversing jalopy
- Rodent catcher allowed to go in rickety vehicle
- Unnerve character returning in rickety old car
- Old banger upset cart
- Unnerve some coming over in old banger
Buddy explains!

The straight part
We know that "old banger" is the straight/definition part of the clue. The straight part is often a synonym or definition, in this case old banger = rattletrap.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 RATTLETRAP mean?
RATTLETRAP noun- A mechanical device, particularly an automobile, that is worn out, run down, or mechanically unreliable as indicated by noises it makes in operation.
- Any piece of miscellaneous equipment or junk.
- Mechanically unreliable or in disrepair.