You don't have anything in your glove box vibrating?

How about something that could have fallen down in the defroster vents?

Aftermarket radio wires hitting something?

 

You know...I have the same vibrating sound in my truck, and I am wondering if it is from my Clifford alarm system. Maybe a shock sensor vibrating against something (aren't they loosely installed?).

La FX4: Do you have an aftermarket alarm installed with shock sensors? Maybe something to look into (I will when it gets warmer!)

 

Did anyone ever figure out what this noise was?