Check all abs wheel speed sensors, they should be a push in till it stops type of a deal, how ever if they do not move freely, DO NOT try to remove them. Often they do seize in the hub if so then you will need to bust out your tools and a few six pack and plan on spendin g a few hours on it. There is generally a collar in the Audi hubs that starts to corrode and lock the sensor in the hub. It requires you to destroy the sensor to get it out. The last option is that some how there is something between the sensor and the exciter ring that is creating the scenario of the ABS activating.
