I don't know if this may be the culprit, but could it be your visor? I know my left visor sometimes vibrates when I hit a bump and makes a sound. Personally, I have no need for a visor because when I flip it down, I can't see the road ahead (let alone traffic lights). What I do to eliminate the sound is pull the visor down slightly so it doesn't bounce off the top.

 

I had to do this exact thing with the '01 I had, because I had the same noise, but the visor is not the problem this time.

Jay