I read a similar problem on a previous posting that was talking about a strut bearing. I really don't have a clue. My hubby has been a mechanic for years and he first thought it might be related to rack and pinion, now thinks it might be related to the traction. [My car has a button you can push to turn traction on/off.] He is stumped, but will follow up on suggestions posted here. [I had a problem with the catalytic converter once and you nailed it.] Got any ideas?