Driver's side window occasionally vibrates on bumps

Vaughanabe13

This is something that just started happening in the last month or so. It started very subtle but it seems like i'm noticing it a little more now. Sometimes, but not always, when I'm going over bumps in the road, I will hear a high frequency rattling coming directly from my left ear. It sounds like it's coming from the window. It's not a loose, floppy rattle, it's more like a micro-vibration of the glass. For some reason it seems to do it more when I'm turning right and going over a bump, but I haven't done any scientific experiments yet to reproduce the rattle. I just had my 15K inspection and an oil change and the dealer said everything looks great, though I didn't bring up the rattle. I don't notice it as much when I have my music cranked up (for obvious reasons) but I don't think the speakers are producing any rattle because I can confirm that it still vibrates with the audio off, and the vibrations correspond to bumps in the road.

FYI this is a 2009 Z34 with sport package, completely stock. Just under 15K miles. Any ideas what this is? I'm not super annoyed with it yet, but it's one of those things that starts to get under your skin after a while.

__________________
2009 Nissan 370Z Touring, w/sport, 6MT, chicane yellow/black.