When I back up in reverse and hit the brakes, there is a loud "clunk" that comes from the rear of the car. Sounds like it comes from passenger side. If i reverse and and keep some pressure on the brake pedal, there is no noise. Any ideas on the problem?

Your rear brakes sound out of adjustment.

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一期一会
Too many people who were born on third base actually believe they've hit a triple.

It's rare, but that problem in my father's '73 /6 Dart turned out to be a bad shock making the noise.