Rattling on driverside window

OK. I've just noticed that the 97 Suburban I just bought has a rattling noise going on while I drive. It appears that the noise is coming from the driverside window when the window is rolled all the way up. I thought maybe that there wasn't a good seal but that doesen't seem to be the case. It almost sounds like a loose wire fluttering around int he wind hitting my door. Any suggestions.

Start simple,
The last bad rattle I had turned out to be some toys dropped in the door pocket.
Easy fix once I found it.