I have a A4 Quat with the 5 speed manual trans. My issue started this morning. When I stop at a light or stop sign and take off again it feels like the front wheels aren’t engaged just the bake, I took off on ice. Half way through the RPM rang of first gear I can hear a slight gear grind noise and it will engage all 4 wheels, again roads where icy and all 4 spin. I just changed the rear diff oil about a week ago and have had no issues until now I used a lucas oil that is a bit heavier than what was in it, maybe that has something to do with it? Is there anything I should check for? Any help would be great ,im new to the Audi world.