Rumbling from rear wheels/suspension on 2001 Audi S4

When the car starts moving from a stop, and especially when coming to a complete stop, there is a rumbling/shuddering noise that comes from the rear wheels/suspension. This only occurs at low speeds coming to a stop, or starting from a stop. This problem is more pronounced in the morning when I first start the car. Can anyone give me an idea of what this is?

Asked by for the 2001 Audi S4
If you have an S4 Quatro, I would suspect the rear wheel drive components such as the inner CV joints.
Thanks dandd, it's gotten steadily worse, I'm taking it in to get it diagnosed today.