Since it was okay before you got on the rough road, I suspect that you lost a wheel weight.
When you have the wheels balanced, MAKE SURE THEY DO A DYNAMIC BALANCE AND PUT WEIGHTS ON BOTH SIDES OF THE WHEEL!!!
I have had massive problems getting the tire stores to balance alloy wheels properly. They insist on putting the weights ONLY on the back of the wheel. This means that they are setting their machine to STATIC balance. This is the same as if you were using a bubble balancer, except you are putting ALL the weight on the back of the wheel which aggravates the dynamic balance.
Another problem you will often run into is that the tire store does not have the correct weight type for the wheels and the ones they use will easily be thrown off. There are two correct wheel weight types for your wheel. The generic one piece weight is a type EN. The best weight is a two piece weight that uses a clip. This is what Mercedes and their dealers use and it is the best way to go.
Failing the correct weight type, a good tire man can use tape weights on both planes by pushing the outer tape weight as far toward the outside as possible and still be on the inside diameter where centrifugal force will keep them in place. A "GOOD" tire man will have no trouble getting this done correctly. If you manage to find a "GOOD" tire man, make a note and tell your friends because they are few and far between.
I have suffered this frustration to a point that I finally bought my own wheel balancer so I could do the job correctly. My cars now have perfectly balanced wheels and are silk smooth to whatever speed I want to run.
Best of luck,