Automatic Transmission Park/neutral Start Switch problems of the 2003 SAAB 9-3

Sudden acceleration. I have a 2003 SAAB 9-3 arc, bought on 9/03, around 13,000 miles, yesterday I went to office and stopped in the right position to park in front of the wall, I stepped on brake, push the gear to "p", all of a sudden the engine started "howling", and accelerated to hit the wall, Im pretty sure that's not the human error, 'cause the gear's in park, and my foot stepped on brake( I have more than 20 years driving experience, to park a car is like normal reaction), I walk out the car, there're two short tire burn mark( if Im not stepped on brake, why does it have the burn mark), so I called my car dealer, they towed the car and try to find out the problem, but it come out the result is nothing wrong with the car! I really want to know if there're anybody has the experiences. Im glad that the thing occurred in front of a wall, if it's in front of a store that might cause lives!!!!! Im afraid of driving my SAAB again; Ill call SAAB tomorrow to find out if they can do something about it? if you need some picture evidence that I took after the thing happen, I can send you by mail!.