I agree on the likely slight wheel imbalance. It must be pretty small if you can't feel it, but can only see it when hands are off the wheel.

If it's easier for you to swap some wheels yourself vs. taking it in for balance, and if your front and rear wheels are the same size, you might try swapping wheels front to back to see if the wobble goes away. If it is so slight on the front, you probably won't notice things at all when the unbalanced wheel is on the back.

And congrats on the straight driving x5.

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2001 X5 3.0i, 203k miles, AT, owned since 2014