GR translation: a hung-up tappet or two

[Mike Jing]

V627.4-8, P639.19-23   Bottles roll clanking on the floor, under the bonnet
a hung-up tappet or two chatters its story of discomfort. Wild mustard
whips past down the center of the Autobahn, perfectly two-tone, just yellow
and green, a fateful river seen only by the two kinds of rippling light.
Roger sings to a girl in Cuxhaven who still carries Jessica’s name:

What does "hung-up" mean here?
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