Calling all Scion tC Owners!

I am a proud owner of a 2007 Scion tC for about 4 months now. Love the car, great all around. But i have noticed one very annoying problem in it and i need some feedback from the other tC owners. Recently i start noticing that there is an annoying noise coming out of the back whenever i am driving on a slight imperfect pavement. To me it sound like the rear hatch but i could be wrong. Its not loud, but loud enough that i can hear it easily. I didnt notice it at first because the weather was warmer and i was driving around with windows rolled down and sunroof up. But now that its getting cooler and i have to keep windows up and the sunroof closed, i can hear it loud and clear.

Now my question is, does anyone else have the same problem? If so, any suggestions of what it could be and can i fix it myself? or do i have to take it to the dealer? I thought at first that it was my license plate, so i put insulation under the plate and mounted it again but that didnt solve the problem. I will really appreciate your help guys. Thank you all in advance.

Sorry about leaving this out, but the sound is something like “dig dig, diggi dig”. Kind of like that. Thanks again you all.

A one year old in the baby seat throwing his voice?

Haha, naw, no babies here (Thank God).

I have a 2005 tC with over 69,000 miles. I absolutely love it. I haven’t experienced that sound, however if you lift the cover over the spare tire commpartment you’ll find a molded styrofoam piece with the spare tire and changing tools as well as some additional cavities. It may be that that fitted piece is loose.