wrenchheader

I have a 91 RHD s13. Completely stock suspension, 18in wheels. My issue is when I hit the right size bump or dip, if feels like my back end jerks over to the right and then feels like it goes right back to feeling planted. Did a visual check at arms and such, but everything seems normal. Happens when driving straight. Everything seems solid if I slalom the car some, just happens on the right size bump or dip. Any thoughts? Its pretty noticeable to the point that my wife asked about it while riding, without me ever mentioning it to her.