I just picked up the original BMW roof rails the other day. As soon as I installed them I took the highway home and started to hear a faint whistling noise as I picked up speed, once I was doing 110/120km/h it sounded like a tea kettle. My panorama sunroof was closed and the tea kettle whistle was just as bad, so loud that my girlfriend couldn't last more than 2 minutes on a phone call. 1/10 for BMW extremely poor design especially considering it's premium price tag. ($400 CAD)

However, I put some hard thought into it and my assumption was that the whistling noise was coming from the inserts that go down the middle of both rails (skinny long opening). I went to my local dollar store and purchased heavy duty water resistant silver duct tape. I was worried it would look like a hack job but it actually came out very nicely.

This process helped a lot with a friend:

1. open up all 4 sides of the rails so that you can see the edges
2. Take silver (or black would look ok, but silver blends very nicely) duct tape, and run 1 long piece from one end of the rail to the other. (Straight, and right down the middle) Keep about 1-2cm of excess tape over the edges and fold it over. The reason why this is important is because it completely seals the opening, and will also block any rain from getting underneath the tape. Also once you close the sides again and lock them you can't see the fold so it looks very neat as well.
3. Press your fingers and slide your fingers down both sides of the tape to seal the sides down and make it look professional. Do not push down on the middle as it will create a small groove in the tape which I personally found to look ugly.
4. Repeat the same process with the other rail
5. Close and lock all 4 edges once the tape is tucked neatly over the edges.

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*IF YOU HAVE THE BIKE RACK OR THE SKI RACK, INSERT THE RACK FIRST AND TAPE THE OPENINGS AROUND THEM. BRING THE TAPE RIGHT TO THE SIDE OF THE RACK ATTACHMENT, AND SAME PROCESS WITH LEAVING 1-2CM TO LIP OVER THE EDGE*

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I would say that this almost completely eliminated the whistling. It's completely silent with the sunroof closed and only a very very light faint wind sound comes when the sunroof is open and only when I'm doing over 120 km on the highway. Hopefully this helps anyone who encountered the same problem as me, as I'm sure it's just the design of the rails. Very frustrating though as I spent as much money as I did and had to spend almost an hour drive home hearing a tea kettle scream in my ear. Thankfully the tape fixed the job. Just do a really neat job, I found doing it with a friend helped a lot and we were able to make it perfectly straight and get both rails done in under 5 minutes.