i have a 2004.5 s40, was driving last night and i stopped at a red light. upon take off after the light changed my car made a loud POP and freaked me out, now it seems to be louder on take off and has a vibration that wasn't there before when accelerating. Anybody know what this could be? I hope it isn't too serious..

 

My first guess would be that it backfired and the exhaust might have taken some damage from that. Have you checked it?

Unfortunately, I'm no expert, but I hope this helps.