I just baught a 2001 Audi A6 4.2 fell in love with the car but the previous owner had an accident. Front bumper is broken and rear right side is damaged figured i could fix that. The car runs gd but it has some problems whenever I turn on the car it makes this huming like sound cant realy tell what it is. When i go between 75-80 mph the car starts to shake (it comes and goes). When i step on the gas i get this smell of amoniac from the engine. Can someone help me?!