rear end sideways jump

Hi all

 My pathfinder is exhibiting a small (and I mean small, more like a wobble) rear end sideways jump when contacting  an imperfection in the road surface. For example a small hole or crack in the surface. Scarey when travelling at speed, but the car immediatly recovers. In addition in some instances the rear end appears to be under damped when running up to a roundabout with those dreaded awareness strips and also exhibits the sideways movement . Checked tyre pressures and shocks but appear to be ok. Any ideas.