I've had my exhaust now for just over three weeks now (SLP), I love the sound of the pipes, but for about two and halfs weeks now I've been hearing a vibration noise coming from under the car at idle (mid section of the car). Does anyone one if this could be related to the exhaust (i.e. because of the exhaust tone its vibrating the car more) .... or could this be something to do with the transmission? I remember reading something about transmission a while back ... It if makes any difference, I got the car mid october, and it has an auto.

 

that was for automatic transmissions on the V6, check your exhaust to make sure everything is properly tightened!