*FIXED* My 96' 850 has developed a terrible rattling some where in the dashboard in front of the drivers seat that only appears over 45-50 mph. There's no rattle of any sort at idle, revving in neutral, or at lower speeds, just when at speeds over 45-50 mph. It sounds like a bee to be honest! I have to make a 3 hour road trip this upcoming Friday at freeway speed and my nerves/sanity may wear thin after listening to the worlds loudest bee under my dash for that long each way... (Not an actual bee, I checked...) Any help is greatly appreciated!
-Luke

 

Are your dash mounts broken? Common issue on these cars.

 

*FIXED* It wasn't the dash at all... The windshield seal trim along the top had a loose edge that was flapping in the wind a little bit whenever the wind caught it or if I went at speeds above 50 mph. A little plastic to metal adhesive and some working in and it's all fixed now. Tested it doing 85 on an empty freeway. No rattle whatsoever.

 

Wow, that's funny.

When I first bought my 855T it had a similar issue, but it was very high pitched squeal, and it only happened above 80-85 mph or so. It was driving me nuts trying to figure out where it was coming from. I even suspected the windshield seal too, but I taped if off and the noise was still there; thought it was the sunroof seal, etc.

Finally looking through the PO's receipts, I see he just had the windshield replaced just before I bought it. So I take it back to the glass place (and kinda pretended I was the PO) and tell them about this crazy squealing noise, and ask them if they've ever heard of such a thing. He says, "Yep, let me take a look at it"... Same thing; he re-glued the outer seal and noise was gone..

 

Weather strip at the top of the windshield.

(Edit: saw you found it.)