I recently noticed when I started it today that it was vibrating and pretty rough for about 5-10 seconds, put it into reverse and was fine. I also noticed a slight knocking noise from under the hood when this was all happening but that stopped within a few seconds of start up. Any ideas what this might be? I recently replaced spark plugs and wires about 2 months ago. It's a 2004 stratus 6cyl.

 

Noise are extremely hard to diagnosis when you can't hear them. The first thought I have about a knocking noise and rough initial idle would be a stuck valve. Does the noise and idle stop at the same time?.

 

My first guess would be either a loose torque converter bolts or a cracked flex plate.

 

Yea it does pretty much. I start the car, it starts vibrating and then I heard the noise from under the hood, then put it into reverse and it all stopped, noise and vibration.