This should be relatively easy to solve. Some areas could be:
1. Tires out of balance or the "bushings" (not sure the technical term) are worn in the steering system.
2. It could be faulty steering dampers. This is a shock that crosses from left to right connecting to tie rod ends. The shock is very firm and you will not be able to actuate it by hand if working properly. usually causes left to right steering oscillation at low to mid speeds.
3. Warped brake rotors for cars with front disk brakes. The rotor hits the caliper every tire rotation causing a small bump in the steering wheel each time.
4. Your tires might need to be rotated and balanced.
5. A bent rim, which balancing will not fix.
Hope you get through...leave some feedback if you get this solved for the benefit of others...