buzzing/vibration

[gsp320 at aol.com (gsp320@aol.com)]

In DC the weather is getting cold - and as such I'm driving with the windows 
closed.  Since I've started doing this, I've noticed an annoying vibration.  
I've traced it to the hood, which buzzes at idle and certain road speeds.  When 
the car is idling, I can press down on the hood a bit (1/4 inch) and it 
stops.
THis happen to anyone else? 
Any idea how to eliminate this?

Thanks, Greg P