We have two of them now, and like every other I've driven, ridden in, etc...silent and solid.
However, from also being on the Aura board a lot, it sounds like one of two common things. 1) The "aluminum look" steel wheels with a plastic cap face can, in limited cases, be defective and create quite a rattle. 2) More so when cold, but sometimes all together if defective, the front struts can rattle--but that wouldn't exactly be too loud. Or, also, as someone said, seriously, something broken, loose, or stuck underneath.
Otherwise, seriously, the Malibu is and has been one of the most solid, quiet, well screwed together GM sedans ever. Not without faults, but I'm guessing one of the top 2 things is possible. Just not sure since I've never experienced it. Any kind of noises drive me nuts and after my G6 that was repurchased, one of the biggest reasons being the roof and sunroof that creaked, popped, and rattled incessantly no matter what was done to it, I was glad to have another Malibu after our first.
Wonder if the neighbor is aware of the squawks his car is making
