Last night I came home from work and just had my car idling. Windows down and ac off I noticed a strange thumping. It happens only when the car is warm and its intermittent. Sometimes it'll happen 4 times a minute and sometimes it'll happen less. It's not coming from the engine though, it's coming towards the rear. It honestly sounds like someone is in the trunk and is kicking it to get out. Tried searching for the same problem but I just find a lot of engine knocking. Anyone have any ideas? Thanks