I have a Tucson PHEV, and every time when I go over a bump, there is a "ding-ding" sound coming from the back of the car. At first I think there is some metal knocking metal under the back cover (in the trunk) but there is nothing, and I cannot find any metal object that is close together that they will hit each other when the car go over the bump. I have also check the back seat storage and sit belts, there is nothing suspicious. Does anyone in this group know anything about this? Thank you.