weird vibration at idle

[turboL]

so my trusty little 3.0 is idleing weird. its vibrates in a fast rythm, but its not so horrible my girlfriend noticed it. also, im running straigth pipes from the header back and when listen tro my exhaust its pulsn too. i didnt mess with any of the o2 sensors and it still has all three cats on it.

 

[Wicked_Sludge]

sounds like its missing a little...which could be caused by a million things. when exactly did it start doing this? was it after any work was done to the vehicle? was it sudden or something that started gradually?