Carrier/rack problems of the 2014 Hyundai Elantra

While driving at speeds up to 55-70 mph, I noticed when I go over potholes the entire backend fish tails. I took it to the dealer I purchased the vehicle from, they could not replicate. This happens every time I hit a pothole, uneven train tracks or uneven road conditions. Took it to another mechanic who couldn't either. Now I'm at another Hyundai dealership who also cannot replicate. I've noticed a lot of people complaining about this and now it's winter. Lots of roads are horrible in illinois and I'm afraid if I hit a pothole while there is snow on the ground that my car will spin out of control and crash. I agree with another complaintant that it will take a death before Hyundai does anything. I saw on car complaints that Hyundai is aware since the 2013 model yet has done nothing. I feel bad for giving the dealership a bad review but someone needs to notice. I do not feel safe and I went back to Hyundai because I had such great luck with my 2003 Elantra, also brand new. I can't say the same about my 2014 Elantra, they look nicer but not sure about the quality under the body. Also noticed that the tires spin on the slightest bit of wet condition, looked that up and the hankook optimos have been given horrible reviews. Might want to rethink the model and tire used, I've owned a no-name brand tire and didn't have that issue. They may not last long but at least I felt safe.