Well, at least you know it's in the front half of your car. From your description this time, I suspect something is out of alignment and that causes a bearing to bind slightly. Try to loosen all screws in the front part of your car by one single turn and see if things are improving. If things improve, check all the plastic parts for damage.
Sometimes, just changing the order in which you assemble parts can make things much smoother. When I first built my serpent impulse, I had a hard time fitting the radio plate on. It just seemed to be too large and wouldn't fit. A quick search on the net gave me the tip to loosen all screws in the front section and try again. It worked.