There was a post on this some time ago, I did a search and could not find it:

I am in the process of trying to find out where the "e body whistle" is coming from:

I taped every exposed moulding edge on the windshield. Still whistles.

I taped over the hood and fender gaps. Still whistles.

I taped over the leading edge of the doors. Still whistles.

The car is covered in green masking tape and the whistle is present and annoying as ever.

I have experienced this in both a 'Cuda and a Challenger, so I think it is safe to say that the noise is not coming from the grill shape or header panel. Could it be coming from the rad support? How about underneath the car?

Has anyone else had this, and, if so, what did you do to fix it?