On the freeway this morning the passenger side rear wheel clunked like I
hit a rock.
It happened 2 more times.
Got off freeway to look at tire.
Pressure around 45, tire looks normal grab and shake-no give.
The belts look OK.
Drive the backroad the rest of the way to work for lower speeds and it
happened  a couple more times.
What can be going on?

Thanks,

Arlene
Wolfsburg 1987 Van