This probably isn't your issue but my wagon had a thumping in the front when turning. It turned out that the wheel weight was rubbing on one of the steering components when the wheel was turned most of the way. The car had been in a front end accident at some point before my time, and something was probably bent just enough that the wieght was rubbing. Had the weight put on the outside of the wheel and no more problem. Look at you wheel weights at see if they've been rubbing.

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