My 2002 Volvo S60 will sometimes rattle/knock when it starts up. This rattling occurs only in park and begins about 10 seconds after the car starts. Sometimes in the initial startup you can tell it is going to do it because the engine RPMs will shoot up to about 2000 but other times it will do it from the normal 1500 RPM startup. If I shift the car into reverse before the rattling starts then the issue seems to go away. Any advice or thoughts on what the cause of this issue might be? A video of the problem can be seen at

 

did u ever find out what it was? mines doing it now :/