I am interested in this "bouncing" problem when on the ground. Can you tell me if it does this constantly, or just now and again? The reason I ask is that I have experienced something similar to this, but it isn't restricted to the CS 707. It also happens with the Flight1 Mustang. However, I believe that the problem is caused by slow loading times. The 707 and Mustang are complex aircraft, and if you are sat at a detailed airport, the sim has to load lots of stuff (textures, models, terrain textures if you are using high res photoscenery, high resolution mesh etc). I suspect that all of this loading causes the sim to "reset the mesh" at intervals as it is loading stuff, which in turn resets the elevation of the aircraft.

Now, I can't be sure this is what causes it. I have noticed that my 707 bounces a couple of times if I am sitting at the runway threshold, and I deploy full flaps (from zero). Again, it's almost as if something is being reset because the extending flaps are altering the airflow calculations required for when the plane starts moving.

Something similar happens with the RealAir Beechcraft Duke after I have landed. As I slow down on the runway, the plane will occasionally "bounce", and cause the "tyre screech" audio to be played, and some touchdown smoke to appear.

In short, if this is the same phenomenon, then I do not believe that it is restricted to the CS 707. It must be something to do with FSX itself.