Strange sound - Transmission Problem?
 

I've had this problem for a few weeks now and it caues no problem at the moment, but I'm trying to figure out exactly what it is.

Right before every gear change (A/T by the way), I hear this sound from the left side of my car that sounds like a glass bottle full of BBs being shook up. Gear changes, sound goes away. It's not that loud either. The time I hear it most is when my window is rolled (oh yesh.. manual windows baby) down.

And I check my transmission fluid frequently, every week or so..

Any idea what this sound is??

Thanks guys.