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Could also be the exhaust system hitting the body. When you put the car into "Drive" the load will cause the drivetrain to shift in the bay a little, but in Neutral or "Reverse" it would center or rock the opposite way, respectively. In some cases, this can cause the exhaust piping to push against the underside of the car and cause a rattle and a vibration under one condition but not the others. Especially if the mount(s) are excessively worn, as mentioned. Best thing is to pop the hood while it is doing it and poke around, then get underneath and inspect everything there.

None of the transmission problems I can think of would realistically be causing this issue without something else much more severe and noticeable during driving, so I think you are probably good there. What is the idle speed running at when you notice the issues?

Rettax3 wrote:Could also be the exhaust system hitting the body. When you put the car into "Drive" the load will cause the drivetrain to shift in the bay a little, but in Neutral or "Reverse" it would center or rock the opposite way, respectively. In some cases, this can cause the exhaust piping to push against the underside of the car and cause a rattle and a vibration under one condition but not the others. Especially if the mount(s) are excessively worn, as mentioned. Best thing is to pop the hood while it is doing it and poke around, then get underneath and inspect everything there.

None of the transmission problems I can think of would realistically be causing this issue without something else much more severe and noticeable during driving, so I think you are probably good there. What is the idle speed running at when you notice the issues?

Usually it's worst at cold when idle is around 1,000 rpm. Put it in Reverse and it makes a big clunk noise followed by the cabin shaking and vibrating but when I move it to Drive is when it quiets down. When warm it does it less but it's still there noticeably.