+1 for HICAS issue. I'm driving a WGNC34 and experienced same symptom. All the sudden the car's rear end becomes wobbly, it feels quite nasty especially at speed of 100km/h+. Mine had some HICAS issues back in last winter, the dash light lit and steering became somewhat odd, hard to describe. Back then I found that the main position sensor of HICAS did have marks of damage (it's basically the lowest part of the car near the diff and can be easily damaged when driving on rough surfaces, gravel or icy snow). The main angle sensor (the one right next to HICAS motor) was cracked on the base of connector and I fixed it then and all went well for a long time but... Well, today the same problem occurred and this time it was very unpleasant. Rear wheels from left to right on random intervals and on every driving speed, usually HICAS comes on when driving something like 60km/h+ but now freaked out all the time car is moving. As I have to drive daily I didn't have time to start checking sensors or the motor, I just disconnected the motor connector and left the whole HICAS off for now. I must continue with the fault diagnosis whenever I have the time. Luckily I have another working ECR33 HICAS to change sensors if needed. And for the record, I have fair shocks, brand new tyres and steering angles adjusted not long time ago. If anyone has ideas of how to continue with the inspection I would be happy to hear.