Random, singular noises don't alarm me: IF, they don't come accompanied by any noticeable change: I just assume something moved due to temperature change, or a flexing of internal surfaces interfacing, etc. Now, if that "crack!" reoccurs, that is a thing. For instance, two days ago, waiting in a parking lot, pointed at the highway, wheels cocked to the left: and I saw a car emerging onto the freeway from the other side and to my right: I accelerated briskly (might have just started to engage the turbos) and heard a rather loud "thump!" come from the LF (inside) corner: my wife said, "What was that?" And we talked about it: how a radical turn from a stand, engaging the turbos, is probably not what the suspension, driveshafts and turbos were meant to do together. Hah. If the car were RWD, none of that would have happened. So, once-off noises that produce no changes are to be ignored, in my humble opinion.
