Omega B – Combi – reversing in the body?

Hi, I haven’t found anything about the search and therefore open a new topic here. I’ve had an Omega B Facelift Caravan since the end of June. I’m actually very satisfied. Only the following problem bothers me: with hard edges in the road like e.g. Gullidecke or bridge overgnage swings/vibrates the whole car a bit. I estimate about 15 Hz. or the same frequency as the one wheel unbalance at 110 kmh. It occurs however independently of speed and speed. d load condition up. On a not quite so good highway it can change to a permanent swing. Of the strength it is so that one can feel it in the seats and the steering wheel partly vibrates. I changed front shock absorbers incl. dome bearings, transverse handlebars incl. jacks and carrying joint and coupling rods. Back only the shock absorbers. After that it felt a bit better, but still there. The driving behavior in curves, brakes etc. is otherwise top. A familiar told me, since ss the omega from the rear axle somewhat swings, but not as much as I describe it. I also think that it comes more from the rear axle, but not only. Does anyone have an idea? can worn-out bushings of the rear axle be the cause? Or can the body generally become soft and have the effect? The omega had 222TKm on the clock when buying and has a retrofitted AHK. How often it was used in the hanging operation is not known. I unfortunately still have no I had to interrupt early in the morning because the bike bolts were not really tight. Thanks already! Many greetings Kai