So did you actually jack it up and wiggle the tire? If you can wobble the tire like that and it has significant move that is most likely a wheel bearing. Not good news! Mine started out really subdued like you mention. But now I hear it on every little tiny bump I hit. It's gotten pretty bad so I'm scheduling a service check-up. I have to drive quite a way to get to my dealership so I've been post-poning.
Although you mention they did something with the shock so I'll bet it's an upper shock absorber bushing. That would make sense. I had a Jeep Cherokee that the upper bushing somehow wiggled out and it was a similar sound but much louder. Maybe the quieter attribute of the car makes it sound less like that.
This thing is less than 3 months in my garage though! They better fix it for free. If you can find the part number that would be great.