Right, I think the noises are from pressure not vacuum build up in the drain that's why the aav made no difference - it only lets air in - If you lift the lid of the manhole in the garden, then run water in the sink and there is no gurgle in the w/m pipes. And vice versa that will verify the theory. Can you identify where the drain run goes to from the manhole away from the house. Also can you see a vent pipe up a wall or through the roof of the house.?