Hi my volvo has been shaking violently and misfiring when started warm, there is also a loud howling noise coming from underneath or the rear of the car while its misfiring. However when i start the car in the morning or on cold days i have no problems at all.(its been really warm the last couple of days when this problem started) I am thinking its the fuel pump or fuel pressure regulator, but hell thats just a wild guess. Any help is appreciated.