I had the annoying buzz from the rear of the car and couldn't figure it out until I was sitting under a bridge waiting for a traffic light to change. A big truck came by and caused the buzz. This lead me to the center brake light fixture - it does have about 1/2 play between the fixture and the window. I cut two small pieces (3/4") of vacuum hose, sliced them down the length of the hose to make a rubber channel, and jammed one on each side of the fixture and the buzz is gone.

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C.G.Mojo