Thud/knock/bump

I have a stock '01 A4 T/A with less than 12k miles on it. Last week it started making this thud/knock type of sound, but only in first gear. For example, I was driving through a Grocery store parking lot, basically idling down a lane. I gave it a little gas and I heard a single knock/thump type sound from the rear of the car. So, I idled down another lane, gave it a little gas, and it did it again. I have tried to replicate it at side street and highway speeds, but it only does it at very low speeds. I checked my tranny fluid, just to see if it may have been low, but it was fine. Any thoughts? Or am I just being paranoid?

Could be a couple of things but the first one I would look at would be the lower control arms. Does it sound side specific?

Until today, I would have said no. But now it seems to be accompanied by a slight rattling sound from the rear passenger side.

I would crawl under there and check the torque on everything and look at your bushings for the lca's, panhard bar, and your end links.

Will do, thanks!