Mr. Crab, that's funny I just had a similar experience with odor in my urine while I was detoxing my liver/gallbladder not from using ACV but from a product I purchased from Sensiblehealth.com. Even so, I think the answer I got from the founder of the website might be helpful in answering your question as well. Here is what I was told:

According to Chinese medicine, any kind of odour is a sign of "heat" in the
body. When there is odour in your urine, it means that "heat" or toxins, are
being released from your body through your urine. Our GCG tincture works by
crushing gallstones. Since Gallstones typically harbour a lot of toxins, by
crushing these stones, our GCG tincture could easily release a fairly large
quantity of toxins into your system. The increased odour in your urine is
likely the result of these toxins being released from your body. As your
Gallstones continue to be crushed and more toxins are released, your urine
should gradually return to normal.