Could be a few things, nothing jumps out at me without driving it, things like this that I'm not sure of I check the siomplest first and work up from there. So in this order I'd check into tires, worn suspension peices, maybe alignment depending on how the first two looked, then have the driveshafts checked and balanced. If possible it might be helpfull to drive the vehicle with the wheels off the ground to observe the spinning parts, obviously this isn't usually a good option for the at home DIYer.
Also by pulsate, where do you feel this? In the steering wheel, seat of the pants, whole vehicle?