I know this might sound very abvious, but have you checked your bumper supports? When I got my car out the shop the last time, I noticed a lot of this from the front and after looking several times, it was only while under the car changing oil that I noticed that one of the braces for the right front bumper was missing. VERY NOTICALBE once spotted! I resecured it with a nut and bolt and all was well. After the car exited the shop for another go around, I noticed the sound. I found this time that the support was completely missing. Very nasty sound!!
Check those bumper cover supports!!
