2002 Volvo S40 Vibration in steering column at low speed ra

After having my vehicle undergo a 4 wheel alignment and tire balancing and rotation, I noticed that it still has a vibration that is transmitted through the steering column and is also transmitted through the floor of the car. The speed range this vibration is most prominent is between 20-28 miles per hour. It dissipates substantially, but is not entirely absent above or below these speeds. The vibration is pulsatile in nature. I should note, however, that the car had an accident with front end damage in the past, mostly affecting the left portion of the vehicle. What is, statistically, most likely the cause of this, and what diagnostic steps can one employ to elicit the etiology of this?