Lexus ES 2007-12 :: Hollow Gong-like Sound When Closing Driver Side Door

I'm still shopping around trying to find the right ES. I test drove a very clean 2008 today save for 2 things. The interior smelled a little stale. Can't figure out if it was cleaning solvents that were used or if it's a cleaning product mixed with light smoker smell. That was the only thing I noticed initially until I got in for a quick test drive and closed the drivers door.

When I closed the drivers door it had a hollow gong-like sound, like if you hit a big empty metal barrel. A 'bung' sound. I haven't noticed this on other ES's I've checked out. You can kind of pick out the noise on the passenger door on this car, but it's very muted. The passenger door sounds like it's supposed to sound. It sounds solid, more 'chunk'. You could pick out the slight 'bung' if you were listening for it, but normally, all you hear is 'chunk'. But, there's no missing it in the drivers door. There's no rattle in the door or the car in general. Initially, I thought maybe the speaker was loose, but nothing is moving in the door, it just 'bungs' when you close it. Maybe it's out of alignment? It looked straight.

Is there sound proofing in the door that could be missing or loose from a repair?