I took my 4Runner to the dealer for the sunroof. They told me that the grinding sound I was hearing is actually the plastic "garnish panel" on the driver's side of the sunroof vibrating. To correct the problem they installed some thicker insulation between the plastic panel and the metal component it attaches to.

A day after I picked up the truck from the dealer service department I noticed that their "fix" was not effective. The plastic panel is still vibrating, but maybe not quite as loud as before.

Besides the incredibly annoying noise this makes I'm concerned as to what is causing this vibration. And why is this only occuring on the driver's side of the sunroof. I found a complaint posted on NHTSA's website describing the same exact problem I'm having, although on a 2003 4Runner.

I'm heading back to dealer service to see if they can get this corrected on the second shot.