Sorry if this is a repeat post but I can't seem to find anyone with quite the same problem as this. I've developed a quite loud "knock" or "clunk" when taking off or accelerating abruptly in 1st, 2nd and even 3rd at times. I just replaced the rear engine mount and this didn't solve the problem. I can feel it almost directly under my feet in the footwell when it happens. It doesn't happen if I drive very carefully and accelerate very slowly, nor does it happen when going over bumps or any other time other than fast acceleration. I can pump the gas pedal and make it clunk nearly on command once I've released the clutch nearly all the way. It doesn't do it in neutral either as I tried to watch the engine in neutral and as a friend drove it and i walked alongside the car. It doesn't vibrate much other than rough idle a bit either. If anyone has any ideas I'm running out of them! Thanks in advance.