The main idea of the sentence is 'I stopped the car', so this is the independent clause. 'When the whistle blew' gives additional information, but isn't meaningful alone. It is the dependent clause.
Whistle when in doubt
The sound of the whistle signaled the start of the track race.
I whistle when I'm scared.Sometimes, I whistle but only make a blowing sound.I whistle to keep a good mood.
The referee blew his whistle to signal that there was a penalty.
Whistle
The nouns are whistle, start, and practice.
He blew a whistle to signal the start of the race.
"when the whistle blew"
The sentence is active because the subject "the noon whistle" is performing the action of announcing lunchtime.
He liked to whistle as he walked.The whistle signalled the end of the match.
He could hear the faint sound of a whistle coming from a distance.
Play is stopped and a goal is not awarded. The restart will depend on the reason the referee blew the whistle.