noticeable single knock when turning left (90 degrees). feel it after starting the engine, when we move the steering wheel. it is the e250 rwd car. has anyone felt something like this?

 

I actually had this. It's slight, correct? More like a "click" in the wheel? Believe it or not, it's the airbag module moving around in the steering wheel! There are several screws that hold it in place, while allowing the horn to be depressed. In some vehicles, the airbag module isn't well retained by those screws, and can actually move. Once you turn the wheel a certain amount, the airbag drops to one side and you can actually feel this in the wheel! Dealer had to replace my physical steering wheel. Haven't had the issue since that was done.