Just the other day my 05 Mazda 3 hatch started to vibrate. It usually occur upon starting up the car and every time I step on the gas while driving. The vibration doesn't occur when the car is in neutral or reverse only when I shift into drive. And it sounds like I have a hole in my exhaust but I checked this by stepping on the gas to rev the engine and it doesn't make any noise. Could it be the engine mount?

 

It was the engine mount! Problem solved!