[BC]

When washing the car ( I30 CW) the other day, I noticed there seemed to be a bit of movement between the 2 panels that join along the trailing edge of the rear wheel arch.  Found there is a phillips head screw joining the panels. It was loose on both sides of the car. 
Would it have eventually dropped out resulting in more body noise over time?  Probably . .
Are there more loose screws I don't know about?  Probably. . .

Checks your screws everyone . . . .

[The Gonz]

Thanks, BC. Good advice. My wife's always telling me I have a screw loose, which keeps me regularly checking. 

[Eureka]

Not too long after buying my car, I found a plastic screw in some of the black plastic trim, under the front bumper, that was not fitting properly.  I took it out.

Edit: just went out to look under the bumper and there is a screw on the right side that is half-way out.  I'll have a closer look tomorrow ...