Hi, I just bought a used Chevrolet Spark from the used car dealer in Singapore. The problem that I hear a rattling sound whenever I engage the reverse gear. I brought this to the mechanic but upon the car engine heated, the problem seem doesn't suffice when I engage the reverse gear. However, we the engine is cold, the problem seem to arise when I engage the reverse gear.
Steel expands when it gets hot, so it isn't a surprise that it stops when the engine warms up. Have you checked to see if there are any loose heat shields on the exhaust or a loose catalytic converter?