If it does this when you take your hands off the bars, then it's the way your front tyre is worn. I've had the same thing happen on past bikes of mine, and it was always because the front tyre was worn.
If it does this while you still have your hands on the bars, then you have other problems.
Really? That is when it happens. When my hands are off the bars. Maybe I'll check the wear on the tire more closely. I dont believe the tires are that old. What would cause uneven wear on a tire? Someone who likes to drive in circles?
[:+1] Check to see if the front tire is "scalloped". That will cause what you describe. Next, check to see if you've thrown a wheel weight. Finally, if neither of those two are the cause, get a dial indicator & check the runnout of the wheel.
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