This ones going to be impossible to figure out but here goes. First the noise is like a quick high chirp sound, maybe a few in a row. It also appears to have a vibration in the mix. Kinda like a rusty pipe sound. Seems to be coming from the road. At first I thought maybe it was the windows but it seems lower on the road but difficult to tell. The stange thing is that I have only heard it on one section of road (so far) that I drive everyday when I drive. Its at the 91 Freeway in Corona California, making the transition to the 71 going south to north. Once the road straightens out. Bam, I hear the sound along this section of the road which I believe is a bridge. Again is a virbration chirp and startled me the first time. Haven't heard it anywhere else. Any thoughts.

 

That's the songbird that belongs to the troll under the bridge. It likes MINIs.

 

Don't be silly, it sounds more like gremlins because there was water on the road.

 

Look under your passenger seat. There is a 1/2" steel bar that runs left to right. This is part of the mechanism that makes up the "memory seat" function that puts the seat back to where it was, when the seat back is tilted. Move it back & forth, and you will see that it rattles like hell. This is where I was getting a high pitched noise, until I dampened it with self adhesive felt. Really lousy design.

 

Maybe road noise if it consistently hits in the same spot. If you can, swap lanes thru that section and see if it changes.