I had a similiar sound from my 2008 malibu.
Took it to the shop and referenced GM TSB Number:060232007 "Clunk, knock or rattle noise from front of vehicle while driving or turning over bumps at low speeds. (diagnose noise - lubricate inner and outer steering shaft, reposition I-shaft, add foam to radiator surge tank mounting bracket"
Got both inner and outer steering shaft replaced and the noise is gone.
Took it to the shop and referenced GM TSB Number:060232007 "Clunk, knock or rattle noise from front of vehicle while driving or turning over bumps at low speeds. (diagnose noise - lubricate inner and outer steering shaft, reposition I-shaft, add foam to radiator surge tank mounting bracket"
Got both inner and outer steering shaft replaced and the noise is gone.
