Hey guys. Well for a while now when ever i turn on my a/c when i first get in my car i hear and feel a really loud like thump come from under the car. kind of like runnig over something but it comes from the engine or under the car when im still. then once the car thumps then some really funky smelly stuff comes out of the vents. kind of like ass?? has this ever happened to any one else. if so please help. thanx.