Is this likely due to worn rotors or wheel balance and alignment issues? There are no noticeable brake issues.
My car has 21000 miles.
My car has an automatic transmission.
The tires could have irregular wear and/or internal belt damage as well as radial force variation. None of that can be balanced "away", excepting that there are road force variation machines that can be used to diagnose radial force variation and possibly make some corrections. The rotors are not likely an issue unless the vibration is occurring while braking. As an experiment, you could try moving the rear tires to the front to see if that lessens the level of vibration. If it lessens the vibration and the front tires are, say, below 5/32 inch of tread, I would just buy new tires, preferably Michelin or comparable high quality.
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