It could be a lot of different things. I had a work truck a couple years ago with the problem. Turned out to be a tire out of balance. A few months later the truck had the same problem and that time it was a tread separation.

It can also be wheel bearings, particularly given the mileage on your vehicle.

I would start by having the front wheels balanced. Alternatively, you could swap your front and rear tires to see if the symptoms change.

Jim Paget
88 YJ with a few changes

www.rrr4x4.com