Well a quick crawl under it will reveal a major structural issue or broken suspension. However there’s a very low likelihood that it’s something like that if it handles fine on the road and then has a little indeterminate thump while stopped. Period.
OP hasn’t been great about replying or adding to the thread. Repeatability is a big part of diagnosis and so far it appears to have happened only twice, yet hard to believe the rig only stopped twice in the last however many miles.
Another suggestion besides manually downshifting if it’s repeatable at multiple stops. (This can literally be done at low speeds in their subdivision or a desolate road ) is kick it into neutral before coming to a stop and see if the thump goes away.
