Hi again,

I had your post hit my email box this morning or maybe yesterday because I don’t let it pester me with notification sounds.
I’m surprised that you haven’t seen more responses from more people that drive and maintain theses cars.
They are newer than my 240’s but I don’t know how many have landed in the hands of owners that do their own work on them.
A person named Klaus helps a lot of peoples cars. Dave Stevens out of Canada is very thoughtful in his post. Follow them for future advice.

Doing the video I’m sure will help attract more attention so I’m hoping that it will help you.
The second one is a lot better in that we actually here that knocking noise. With you being in the drivers seat does match up to where most of us get our information also.

It definitely repeats itself nicely to say that the engine is shifting it position on it mounts in the opposite direction of driving forward. For me that’s a good clue.
When that happens the months are a top suspect along with things attached to the engine like exhaust pipes or lines.
Have you had any work done on the car recently that may have moved a component closer to a body point?
With this thought I used the idea of use having a date with a 2x4 or a pry bar to wiggle the engine on it mounts. Especially in the opposite direction of torque or twist to the direction of the wheels rotating going forward.
You may have to get an assistant to put the car directly into reverse and out while observing under the car. Check on the back of the engine and each of mounting points that have rubber joints.
I have read that a upper mount near the front of the car goes soft rather regularly and it’s not hard to change. I will hope for you that it’s that mount.

Can you tell if the sound is coming from your feet or up higher behind the dash? Left or more right?
If it’s low and in the center then that area is going to be harder to see from above.

Make sure that when ever you are running the engine that you can keep the car from moving!

From what I can tell from the video it does not sound internal to the transmission or engine because it varies so much and only in reverse.
The noise of the engine itself seems a little higher than normal but with a high mileage vehicle, that is always an area of contention.

Hope you find it.

Phil